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The present work was performed on experimental Al–Si near eutectic cast alloys, with different additives mainly Fe, Mg, Mn, Cr, Sr and P. The alloys were solidified at 0.8°C/s, very close to equilibrium conditions. Precipitated phases, primarily Fe-, Cu-, Mg-, and Sr-based intermetallics, were examined. Although the phases reported in the present work were documented previously, the range of chemical composition of each phase was confirmed using an electron probe microanalyzer (EPMA) equipped with wavelength dispersive spectroscopy (WDS) and electron dispersive X-ray spectroscopy (EDS) facilities. Some of these alloys were cast in the form of hardness test pieces using a steel permanent mold preheated at 425 °C that provided a microstructure with an average dendrite arm spacing (DAS) of ~22 µm. The test pieces were solution heat treated at 500 ± 2 °C for times up to 24 h, followed by artificial aging at 155 °C for 5 h (T6 treatment). Hardness tests were carried out on the heat-treated test pieces. It was found that addition of Sr decreased the hardness. The role of P addition (AlP) on the nucleation of primary Si particles has been discussed. Although the addition of P in terms of 30 ppm leads to refining of the primary Si particles, the P-Sr interaction has a marked negative effect of the modification of the eutectic Si particles. [ABSTRACT FROM AUTHOR]

Abstract The effect of the addition of Zr, Ni, and Mn and the elevated temperature thermal exposure on the mechanical performance (tensile and hardness properties) of Al-Si-Cu-Mg cast alloy were investigated for this research study. The evolution of the strengthening precipitates during the prolonged thermal exposure were also investigated using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) in order to correlate the variation in the mechanical properties to the nature of the strengthening precipitates. Varying the thermal exposure technique from static into dynamic had little effect on the tensile and hardness data obtained at room temperature. This permitted using the static exposure (stabilization) technique to simulate the behavior of the material under dynamic thermal exposure conditions as in the case of the automotive engine components. Coarsening of the strengthening precipitates following prolonged exposure at 250 °C had a deleterious effect on the tensile properties and hardness values. Noticeable reduction in the strength values, particularly the yield strength, and a remarkable increase in the ductility values were observed. The coarsening kinetics of the precipitates decayed with time, due to the continuously increased distance between the precipitates with increase in the exposure time, causing the observed deterioration in the mechanical performance after exposure at 250 °C up to the first 100 h. However, further thermal exposure up to 200 h did not result in further reduction in the strength and hardness values. [ABSTRACT FROM AUTHOR]

In this article, the volume fraction of intermetallic compounds in Zr-containing 354-type Al-Si-Cu-Mg alloys, characteristics of eutectic Si particles, and tensile, hardness, and impact properties have been evaluated with varying Ni and Mn contents and combination. The results revealed that additions of Ni and Mn in different amounts and combinations increased the volume fraction of intermetallic compounds in the tailored alloys, compared to the base alloy (cf. 12.21% for 4% Ni-containing alloy with 2.5% for base alloy), producing a significant effect on the mechanical performance. The proposed additions enhanced the mechanical performance of the alloys, namely, the ambient- and elevated-temperature tensile properties, hardness values, and impact properties. For the Mn-containing alloys, the improvement in properties was attributed to the formation of sludge particles in the form of blocky α-Al15(Fe,Mn)3Si2 alongside the script-like α-iron phase that resisted crack propagation. The precipitation of Ni-bearing phases such as Al9FeNi, Al3CuNi, and Al3Ni in the Ni-containing alloys improved the mechanical properties through hindering cracks propagation. Interestingly, addition of 0.75 wt.% Mn to the base alloy proved to be competitive in strength values to the addition of 2 and 4 wt.% Ni, and better in terms of ductility values. The investigations showed that the variations in hardness and impact values follow the same trend as variations in the percentage volume fraction of intermetallic compounds, i.e., maximum property value is associated to the alloy with highest volume fraction of intermetallic compounds. Furthermore, the impact properties showed higher dependency on Al2Cu phase particles rather than the eutectic Si particles. [ABSTRACT FROM AUTHOR]

The present study was undertaken to investigate the capacity of the ultrasonic technique for measuring various particles in liquid aluminum and commercial 356 alloy at two different temperatures each. Particles of TiB2, AlSr, Al3Ti, and Al2O3 were studied using a Metalvision MV20/20 ultrasonic machine. The data provided plots of (1) the cleanliness value, (2) average particle size, and (3) particle count for each particle size range, as a function of testing time. An examination of the microstructure of solidified samples obtained from samplings of the melt was also carried out using Jeol JXA-8900L electron probe microanalyzer. Other techniques, including the liquid metal cleanliness analyzer and all the filtration techniques, can only detect TiB2 particulates when the concentration is very low (less than 10 ppm B). By applying the ultrasonic technique, measurements may be conducted properly for concentrations as high as 90 ppm B; thus, the ultrasonic technique provides an improved alternative for the measurement of TiB2 particulates in liquid aluminum. This fact is of significance, since particles are invariably present because the addition of TiB2 is essential to the grain-refining processes used for aluminum alloys. [ABSTRACT FROM AUTHOR]

The effects of several variables on the precipitation of the β-AlFeSi phase, and porosity formation in A319.2 alloys were examined in detail. Various techniques were used for microstructural characterization and phase identification, including optical and scanning electron microscopy, electron probe microanalysis coupled with energy-dispersive X-ray and wavelength-dispersive spectroscopy facilities, and thermal analysis. An image analyzer was used in conjunction with the optical microscope for quantification purposes. The results obtained showed that the amount of iron present in the alloy affects the size of the β-AlFeSi platelets and their distribution, particularly at low solidification rates. Addition of strontium leads to fragmentation of co-eutectic or post-eutectic β-platelets. This effect diminishes with the increase in iron concentration, and further strontium addition leads to the precipitation of AlSiSr phase particles, instead. The porosity observed at any given iron level is the result of the competition between fluidity and β-platelet size and depends on the permeability of the interdendritic regions as solidification proceeds. Although branching of the β-platelets leads to porosity formation, the platelets, on the other hand, also limit pore growth. In general, percentage porosity, maximum pore area and maximum pore length increase with an increase in the average maximum β-AlFeSi platelet length. In the Sr-modified alloys, porosity formation is frequently associated with strontium oxides (particles or films), as well as the β-AlFeSi platelets. These oxides (with a stoichiometric composition close to AlSrO) are formed during melting, due to the high oxygen affinity of strontium, and are difficult to remove via degassing. [ABSTRACT FROM AUTHOR]

The principal aim of the present research study was to investigate the effects of minor additions of zirconium on phase precipitation in 354 alloys under very slow solidification rates. The results showed that reactions corresponding to precipitation of Cu-containing phases are also observed in the 354 alloy at temperatures below 500 °C. Zirconium reacts only with Ti, Si, and Al. The Zr-rich intermetallic phases observed in this study appear in two different forms: the phase (Al,Si)(Zr,Ti) containing high levels of silicon which is block-like in form, and the phase (Al,Si)(Zr,Ti) containing high levels of aluminum, which appears in needle-like form. There is no observable poisoning effect on the refinement of grain size after the addition of Zr to the alloys investigated, as was observed from the macrostructures of the thermal analysis samples obtained at high solidification rates, for the alloys containing Zr and Ti. In thermal analysis experiments carried out at the higher solidification rate, namely 4 °C s, there is an observable reaction within the temperature range of 667-671 °C which appears to be related to the precipitation of Zr-rich phases; it was not possible to observe this reaction at the lower solidification rate of 0.35 °C s generally used in thermal analysis. [ABSTRACT FROM AUTHOR]

The present study was carried out to investigate the effects of Ni (high and low), Mn, Zr, and Sc additions, individually or in combination with other additives, on the microstructure and tensile properties of 354 casting alloy (Al-9 wt% Si-1.8 wt% Cu-0.5 wt% Mg) at ambient temperature following aging in the temperature range 155-300 °C for different aging times. Solution heat treatment of the studied alloys improves the tensile properties and alloy quality of all alloys. The presence of Ni and Zr (with no Cu), and Sc and Zr provides improvement as these alloys show the best YS values. Multiple aging peaks are observed in the age-hardening curves of all studied alloys, related to the precipitation sequence which occurs in each alloy. The best combination of properties is achieved after aging at 190 °C/2 h for all alloys studied, with the exception of the alloy containing 2 % Ni + 0.25 % Zr that showed the best combination at 190 °C/4 h. These conditions may therefore be considered as the appropriate T6 heat treatment parameters for these alloys. Under the experimental conditions of the present study, aging at 190 °C (for 2 or 4 h) introduces a technologically useful strategy for this particular alloy system as it provides a significant economic benefit in the form of a noticeable reduction in the aging time required to reach peak strength. [ABSTRACT FROM AUTHOR]

The present study was carried out to investigate the effects of minor additions of Ni and Zr, individually or in combination, on the microstructure and tensile properties of 354 casting alloy (Al-9 wt%Si-1.8 wt%Cu-0.5 wt%Mg) at room temperature (25 °C/77 °F) and at high temperatures (155 and 300 °C/311 and 572 °F) using different holding times at testing temperature. An analysis of the data obtained from microstructural and tensile tests shows that the tensile behavior of 354-type cast alloys is strongly influenced by the testing temperature and the holding time at temperature prior to testing. The effect of minor additions of Ni and Zr on the high-temperature performance of these alloys is controlled by their T6-properties at room temperature. The addition of 0.2 wt% Ni and 0.2 wt% Zr improves the T6-tensile properties considerably, compared to the as-cast condition. The addition of 0.4 wt% Ni + 0.4 wt% Zr is not sufficient to resist softening at 300 °C (572 °F)/100 h. The addition of 0.4 wt% Ni to alloy 354 leads to a decrease in the tensile properties, attributed to a Ni-Cu reaction that interferes with the formation of AlCu strengthening precipitates and affects the age-hardening process. The fine L1 (Al(Zr,Ti))-type precipitates is the main feature observed in the microstructure of alloys containing 0.2-0.4 wt% Zr additions. The presence of Q-AlCuMgSi phase and AlNi phase is observed in samples tested at 300 °C (572 °F) after 10 h holding. [ABSTRACT FROM AUTHOR]

The aim of the present work was to investigate various means of obtaining a fine eutectic silicon structure in A356.2 alloy and therefore improve the alloy mechanical properties. The effects of solidification rate, Sr modification and melt thermal treatment (MTT) on the silicon particle characteristics of A356.2 (Al-7 %Si-0.4 %Mg) alloy were studied. The particle characteristics measured were the average particle area, average particle length, average particle roundness and average particle aspect ratio, using image analysis and optical microscopy. The results showed that Sr modification-, superheat- and Sr modification-MTT (SrMTT)-processed castings provide fine eutectic Si particles, the SrMTT process giving the best modification results. Both size and morphology of the eutectic silicon particles are affected by the modification process used. The Sr-grain-refined, Sr-melt superheat and SrMTT castings show well-modified fibrous Si particles, whereas the MTT casting exhibits Si particles that, although refined to a certain extent, still retain their acicular morphology. Solidification rate affects the eutectic Si particle size in that a higher solidification rate produces finer Si particles. However, within the range of solidification rates provided by the end-chill mold used in this work, the solidification rate does not affect the morphology of the Si particles. [ABSTRACT FROM AUTHOR]

The present work was performed on low Fe-low Mg A319 alloys. The results show that the A319-type aluminum alloy with the optimum combination of impact properties consists of a Sr-modified alloy with additions of Mg. The Sr-modification process does not affect the aging behavior of the alloy, while the addition of Mg enhances its response to artificial aging. The strengthening effect observed in the alloy is due mainly to the presence of θ-AlCu particles which precipitate in the form of needles and plates. The degree of strengthening that may be obtained depends directly on the amount and homogeneity of the θ-AlCu phase. The alloy does not exhibit the common peak-overaging conditions normally found in the literature. This is due to the presence of sequential precipitation of different species during the aging process, whereas hardness is less sensitive to melt treatment conditions, and aging treatment has a significant influence on the alloy hardness. In the non-modified alloy, the Si particles may be cleaved during impact testing resulting in poor toughness. Modification with Sr improves the alloy resistance to fracture during impact testing due to the larger volume fraction of the ductile aluminum matrix compared to non-modified alloys. [ABSTRACT FROM AUTHOR]

The grain refining influence of Ti and B in the presence of Sr was investigated in A356.2 alloy using Al-10 wt%Ti, Al-5 wt%Ti-1 wt%B, Al-2.5 wt%Ti-2.5 wt%B, Al-1.7 wt%Ti-1.4 wt%B and A1-4 wt%B master alloys. Strontium modification of the A356.2 alloy was carried out using Al-10 wt%Sr master alloy and two levels of Sr: 30 ppm and 200 ppm. The occurrence of intermetallic phases resulting from Sr-Ti and/or Sr-B interactions was investigated using electron microprobe analysis and metallographic techniques. Addition of B in amounts exceeding 0.1 wt% led to the formation of particles containing predominantly B and Sr, with a composition approaching SrB. No interaction between Sr and Ti was observed. Thus, the boron content of the alloy should be considered as one of the parameters which would affect successful grain refinement and modification of A356.2 castings. The effect of Sr/B interaction on the grain size of the A356.2 alloy samples is also presented. [ABSTRACT FROM AUTHOR]

The present study was performed on low magnesium A413.0 type alloys. The results show that strontium (Sr) is mainly concentrated in the silicon particles. Overmodification occurs when Sr precipitates in the form of Al2SrSi2, which takes place over a wide range of temperatures. The first peak occurs following the precipitation of α-Al, the second peak is merged with the precipitation of eutectic silicon (Si), and the third peak is a posteutectic reaction. Introduction of phosphorus (P) to Sr-modified alloys leads to the formation of (Al,P,Sr)2O5 compound, which reduces the modification effectiveness of Sr. Therefore, in the presence of P, the amount of added Sr should exceed 200 ppm. For the same levels of P, the tensile parameters of well modified alloys (233 ppm Sr) are relatively higher than those partially modified with Sr (about 60 ppm Sr) containing the same amount of P. During solution heat treatment, coarsening of the eutectic Si particles occurs by the growth of some particles at the expense of the dissolution of the smaller ones, as well as by the collision of nearby particles. [ABSTRACT FROM AUTHOR]

Highlights: [•] Impact properties of Sr-modified A356.2 alloys using various grain refiners. [•] Addition of Ti and B greatly improves toughness of fully modified alloy. [•] Highest toughness obtained for T6-alloys with Al–5%Ti–1%B and Al–10%Ti master alloys. [•] Sr–B interaction may result in significant deterioration in impact properties. [Copyright &y& Elsevier]

The effects of melt treatment in particular the types of grain refiners as well as Sr modification on the impact properties A356·2 alloys in as cast and heated treat conditions have been investigated. The results show grain refining is very effective parameter in improving the alloy toughness when the alloy is well modified. The best values for total absorbed energy of T6-tempered alloys are achieved after using 0·04%Ti in the form of Al–5%Ti–1%B and Al–10%Ti master alloys. A significant degradation in impact properties is observed due to the Sr–B interaction in some cases leading to the formation of Sr6B compound. The improvements in toughness are mainly due to the change in silicon particle morphology and to the dissolution and fragmentation of intermetallics during the solution heat treatment process at 540°C for 8 h prior to quenching and artificial aging. [ABSTRACT FROM AUTHOR]

Abstract: An extensive study related to the investigation of the precipitation behavior of the CuAl2 phase in various 319-type alloys containing strontium (Sr), iron (Fe) and phosphorus (P) alloying elements, and its dissolution during solution heat treatment at 490 °C for times up to 100 h was carried out in the present work. Furthermore, the effect of CuAl2 and other intermetallics on the alloy performance under two different heat treatment conditions (i.e. T5 and T6) was also investigated through an examination of the tensile and impact properties. By comparing the experimental results, conclusions were drawn in terms of the optimum alloying elements, solidification parameters and heat treatment conditions (viz., Sr modification, Fe content, cooling rate and T6 condition). The fracture behaviors of the 319 base alloy and the Sr-modified 319 alloy containing ∼1.2% Fe were also compared through a study of the fracture surfaces of the corresponding alloy samples. The results explicitly reveal that solution heat treatment plays a critical role in the dissolution of the CuAl2 phase. Iron addition leads to an increased precipitation of brittle β-Al5FeSi platelets which act as preferred crack sites and dramatically reduce the impact properties, regardless of the value of dendrite arm spacing. Crack initiation usually occurs through the fragmentation of Si particles and β-Al5FeSi platelets, and the crack propagates through the cleavage of β-Al5FeSi platelets. [Copyright &y& Elsevier]

Highlights: [•] The tensile curves could be divided into four main regions depending on the applied solution temperatures. [•] The porosity measurements support the tensile property results. [•] High solution temperature also produces macrocracking and buckling. [•] Macrocracks are observed in bars containing Mg in the order of 0.1%. [ABSTRACT FROM AUTHOR]

The present study was undertaken to investigate the effect of Mg on the occurrence of incipient melting in experimental and industrial 319 alloys using thermal analysis, tensile testing, microstructural analysis and porosity measurements. Castings were prepared from experimental and industrial alloy melts containing Mg levels of 0-0·6 wt-%. The addition of Mg leads to the segregation of the copper phase, resulting in the formation of the block-like form of the CuAl2 phase rather than its finer eutectic-like form. This makes it more difficult to dissolve the CuAl2 phase during solution heat treatment. The addition of Mg to 319 alloy, irrespective of the alloy source, modifies the Si particle morphology. This effect is observed very clearly at 0·6 wt-%Mg, with a corresponding decrease in the Al-Si eutectic temperature compared to the base alloy. As expected, the modification effect of Mg is not very obvious at low Mg addition. The addition of Mg also leads to the precipitation of the Al5Mg8Cu2Si6 phase. This phase normally precipitates after the CuAl2 phase. Nevertheless, when the addition of Mg exceeds 0·4 wt-%, the precipitation of the Al5Mg8Cu2Si6 phase also takes place in another reaction, before the precipitation of the CuAl2 phase. The morphology of the Al5Mg8Cu2Si6 phase particles in this case is script-like rather than the irregular shaped particles normally observed. [ABSTRACT FROM AUTHOR]

The present study was undertaken to elaborate on the parameters controlling the microstructural characterization of A319.2 Al–Si alloys, as a function of iron content (0.12–0.8%), Sr addition (~250 ppm), and solidification time (586s vs 513s). For comparison, selected conditions were applied to A356.2 alloys. The use of a hot graphite mold and an end-chill mold provided different solidification rates along the liquid/solid interface, corresponding to DAS values in the range of ~23–85μm, corresponding to levels of 5, 10, 30, 50, and 100 mm above the chill end. Addition of strontium leads to fragmentation of β–Al5FeSi platelets. Under similar Fe level and solidification rate conditions, the A319.2 alloys exhibit larger pore sizes than the A356.2 alloys, due to the absence of the (Al–Al2Cu) reaction in the latter and hence longer solidification time. Four types of iron intermetallics were reported viz., δ-, α-, β-, and π-phases. [ABSTRACT FROM AUTHOR]

Abstract: DTA analysis was used to investigate the solidification reactions of alloy A319 with either 12 or 136ppm of Sr added. Strontium does not affect primary solidification of (Al) dendrites but modifies the kinetics of the (Al)–Si eutectic. The effects of Sr level and of cooling rate on the characteristic temperatures for the (Al)–Si and other eutectic reactions are described. [Copyright &y& Elsevier]

Light aluminum alloy engine blocks have successfully replaced heavy ferrous materials in order to enhance automobile fuel efficiency. Aluminum engine blocks with gray iron cylinder liners are prone to tensile residual stresses along the cylinder bridges, which may cause distortion and reduce engine efficiency. In this study, the sectioning technique was used as a means for measuring average residual stresses in critical regions in engine blocks subjected to different metallurgical parameters. It was found that the stresses could be higher than 100 MPa in tension after casting. Relaxation of residual stresses was observed after solution heat treatment, freezing treatment, and aging compared to the initial stage, depending on the geometry and size of the workpiece. Relaxation rate was found to be affected by the size of the workpiece. [ABSTRACT FROM AUTHOR]

Thermal analysis of various 354 alloy melts was carried out to determine the sequence of reactions and phases formed during solidification under close-to-equilibrium cooling conditions. The main reactions observed comprised formation of the α-Al dendritic network at 598 °C followed by precipitation of the Al–Si eutectic and post-eutectic β-Al5FeSi phase at 560 °C; Mg2Si phase and transformation of the β-phase into π-Al8Mg3FeSi6 phase at 540 °C and 525 °C; and lastly, precipitation of Al2Cu and Q-Al5Mg8Cu2Si6 at 498 °C and 488 °C. As a result of the low solidification rate of the thermal analysis castings, all Zr-containing alloys are located in the L + Al3Zr region of the Al–Zr phase diagram during the melting stage. Three main reactions are detected with the addition of Ni, i.e., the formation of AlFeNi, AlCuNi and AlSiNiZr phases. Larger sizes of AlFeNi and AlCuNi phase particles were observed in higher Ni content alloys of 3.6 wt%. Mn addition helps in reducing the detrimental effects of the β-iron phase by replacing it with the less-detrimental Chinese script α-Al15(Fe,Mn)3Si2 phase and sludge particles. With the use of the multi-step solution treatment—involving higher solution temperatures and longer durations, an increased amount of incipient melting is likely to occur. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the mechanical properties of a newly developed aluminum Al-6.5% Cu-based alloy, coded HT200, as well as to determine how these properties can be further improved using grain refinement and heat treatment. As a result, the effects of different heat treatments and alloying additions on the ambient and high-temperature tensile properties were examined. Three alloys were selected for this study: (i) the base HT200 alloy (coded A), (ii) the base HT200 alloy containing 0.15% Ti + 0.15% Zr (coded B), and (iii) the base HT200 alloy containing 0.15% Ti + 0.15% Zr + 0.5%Ag (coded C). The properties of the three HT200 alloys were compared with those of 319 and 356 alloys (coded D and E, respectively), subjected to the same heat treatment conditions. The results obtained show the optimum high-temperature tensile properties and Q-values for the five alloys of interest, along with the corresponding heat treatment conditions associated with these properties. It was found that the T6 heat-treated alloy B was the optimum alloy in terms of properties obtained, with values comparable to those of commercial B319.0 and A356.0 alloys. [ABSTRACT FROM AUTHOR]

The present study was performed on an Al-6% Cu-0.7%Si alloy, and 319 and 356 alloys following different heat treatments. The main task was to evaluate the drilling and tapping characteristics of the Al-Cu alloy with respect to the Al-Si-based 319 and 356 alloys. The drilling work was carried out on a Huron K2X8five CNC machine at 15,000 rpm with continuous cooling to absorb the heat and to clean the holes from the chips formed during the drilling operation. The results show that the addition of Si coupled with T6 aging treatment produces the highest cutting forces (about 360 N) among the alloys studied (approximately 270 N) after 2500 holes. Considering the Al-Cu-based alloys, varying the aging treatment has practically no significant bearing on the cutting forces. Apparently, a high Cu content acts as a self-lubricant, facilitating the drilling process up to 2700 holes, with no sign of tool wear. However, due to the low level of Si in the Al-Cu-based alloy, built up edge (BUE) is more frequent, with conical chips, which would affect the precision of the size of the drilled hole. The chips are normally dull and characterized by their rough surfaces compared to those obtained from A356.0 alloy. Tapping of the drilled holes was carried out using Guhring 971 H6 M6 6HX- HSSE taps. The HT200-based alloys revealed excellent machinability with no sign of tool wearing after 2500 holes. In contrast, the tool failed after 1600 holes in the case of 356 alloy and 2160 holes for 319 alloy. Thus, it is concluded that the presence of 3.5% Cu in the 319 alloy helped in reducing the severity of wearing due to eutectic Si particles. However, the tapping forces reached 120 N prior to failure compared to about 75 N in the case of T200-based alloys. [ABSTRACT FROM AUTHOR]

This study investigated the effects of adding Zr, as a base alloying element, besides Ni and Mn in different amounts and combinations on the melting and solidification characteristics of 354-type Al-Si-Cu-Mg alloys. Differential scanning calorimetry (DSC) was used to characterise the sequence of reactions occurring during the heating and/or cooling cycles; whereas scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques were used to observe and identify existing intermetallic phases. Nickel proved to have a retarding effect on the kinetics of precipitation of the α-Al network and the eutectic Al-Si structure. Also, the presence of Ni consumed a considerable amount of Cu to form Al-Cu-Ni particles instead of Al2Cu particles. Results revealed that solution treatment at 495°C for 5 h was sufficient to dissolve a large amount of Al2Cu particles in the α-Al matrix, which is mandatory for a successful aging treatment of the alloys studied. Additions of these transition elements produced new intermetallic phases such as (Al,Si)3(Ti,Zr), (Al,Si)3Zr, Al9FeNi, Al3Ni, Al3CuNi, and Al9FeSi3Ni4Zr, in addition to the other phases, namely α-Al, eutectic silicon, Al2Cu, Mg2Si, Q-phase (Al5Cu2Mg8Si6), commonly observed in 354-type alloys, and Fe-based intermetallic phases including β-Al5FeSi, α-Al15(Fe, Mn)3Si2, and π-Al8FeMg3Si6. Superheating the melt at 800°C instead of 750°C had an advantageous effect in that Al3Zr particles originating from the Al-15%Zr master alloy were dissolved and hence coarse Zr-containing particles were barely spotted in the microstructures examined. [ABSTRACT FROM AUTHOR]

Most designers take into consideration the stresses that act on a material but despite safety considerations, failure may occur due to other factors that were neglected in their design. These factors can be a pre-existing flaw, microstructure deficiency or the presence of residual stresses. Depending on the stress type, residual stresses combined with applied stresses can aid or hinder failures. Consequently, reducing the amount of residual stress can have a promising effect on the life of the component. Different casting parameters can change the microstructure and residual stresses of castings. In this research, the relation between residual stresses and microstructure evolution under the influence of different casting parameters was investigated, using both Al-Si-Mg (Al-356) and Al-Si-Mg-Cu (Al-319) alloys. Solidification rate, quenching rate, aging temperature and aging time were the main parameters considered for this study. The results indicate that the magnitude of the residual stresses increases with increasing solidification rate and quenching rate. Also, the residual stress relieving is proportional to the aging temperature [ABSTRACT FROM AUTHOR]

The present study was carried out on ultra-pure aluminum, 1050, and 356 alloys. The results revealed that when Al-4%B is added to ultra-pure aluminum, it forms AlB12 and AlB2 which have no grain refining effect in pure aluminum. When no grain refiner is added to pure aluminum, the microstructure is a mixture of columnar and equiaxed grains. The addition of 30 ppm Ti to pure aluminum is sufficient to promote equiaxed grains when the metal is solidified at high rate ~ 10°C/s but requires an addition of 1000 ppm B at 0.8°C. Increasing the Si content to 7% reduces the initial grain size of pure aluminum from 2800 μm to 1200 μm. In commercial aluminum, B reacts with traces of Ti to form TiB2 phases which are active grain refining agents. However, in Al-7%Si, Ti reacts with Si forming (Al,Si)2Ti phase which is a poor refining agent. [ABSTRACT FROM AUTHOR]

A study on the effect of different grain refiners and addition technique in Al-7%Si alloys was carried out. The results show that the Al3Ti phase reacts with silicon (Si) in the molten alloy forming a new compound (Al,Si)3Ti. This reaction is independent of the grain refiner addition technique. The temperature of the liquid metal causes a significant change in the Al3Ti phase morphology, which precipitates in the form of platelets at 750°C and in a dendritic form at 950°C. It has also been observed that while (Al,Si)3Ti phase platelets precipitate within the α-aluminum dendrites, the TiB2 or AlB2 particles are rejected into the surrounding interdendritic regions. The results also reveal that addition of 100ppm B will reduce the initial grain size by ~ 85%, which is more than the reduction obtained with the addition of 0.2%Ti in the form of Al-10%Ti (about 65%). [ABSTRACT FROM AUTHOR]

The present study was performed on the 354 (Al-9wt%Si-1.8wt%Cu-0.5wt%Mg)-based alloy to which measured amounts of Zr, Ni, Mn and Sc were added. Tensile test bars were prepared from the different 354 alloys using an ASTM B-108 permanent mold. The test bars were solution heat-treated using a one-step or a multi-step solution heat treatment, followed by quenching in warm water, and then artificial aging employing different aging treatments. Tensile bars were thereafter tested at 25 and 250 °C. Analysis of the tensile data was carried out using quality charts and color contour maps. The results show that at room temperature, Alloy R (354 + 0.25%Zr) showed the best quality index values after T6 treatment, i.e., 411 and 418.64 MPa without, and with 200-h stabilization at 250 °C, respectively. Alloy U (354 + 0.25%Zr + 0.75%Mn) displayed a Q-value of 397.84 MPa after T6 treatment (with no stabilization) and 404.62 MPa following T6 treatment and 200-h stabilization at 250 °C before testing. At 250 °C testing temperature and after 200-h stabilization at 250 °C, the strength of all alloys exhibited a decrease in strength with an increase in ductility being related to the softening, which occurred due to the onset of overaging. [ABSTRACT FROM AUTHOR]

In the production of high-quality aluminum castings, melt cleanliness is important in regard to the performance and quality of the cast part and is determined, among other factors, by the inclusions present in the molten metal. Besides causing problems in process and quality control, other harmful consequences include reduced mechanical properties, poor machinability and increased porosity. Thus, control of melt cleanliness requires monitoring and minimizing the presence of impurities and inclusions. The liquid metal cleanliness analyzer (LiMCA) technique was used in the present study to investigate its capability for measuring inclusions such as Al2O3, Al4C3, MgO, CaO, TiB2 and TiAl3 typically found in aluminum alloys, where these inclusions were added to Al-6%Si alloy melts using powder, master alloy, pure metal and metal matrix composite sources. Melts containing the different inclusion types were prepared, and the melt cleanliness was quantified using the LiMCA technique. Samplings for microstructural examination were also taken simultaneously. Evidence of the agglomeration of a vast amount of TiB2 inclusions as captured by the LiMCA probe tube shows that LiMCA is the only technique that is able to capture such agglomerates in-line, without any problem, as other techniques such as the PoDFA and Prefil cannot measure such TiB2 agglomerates without their filter systems getting clogged and interrupting the measurements. This is a significant finding and demonstrates a very important aspect of the LiMCA technique, particularly in view of the fact that Al-Ti-B master alloys are regularly employed for grain refining aluminum casting alloys. [ABSTRACT FROM AUTHOR]

Qualiflash is a quick method of assessing the melt cleanliness of foundry Al-Si alloys over a wide range of Si contents up to 17 wt%. It has an immediate response in measuring the quantity of oxides and non-metallic inclusions. Improving the melt cleanliness moves the Quality Temperature Index line toward lower Q values. Prefil curves demonstrate very good sensitivities to the variations in the melt treatment conditions. The filtration rate is greatly affected by grain refiner addition. The highest curve is displayed by the alloy without grain refiner addition. The filtration rate progressively decreases with increasing amount of grain refiner. When the total amount of boron in the grain refiner added to the melt reaches 60 ppm, the filtration rate is approximately nil. The overall error on the Prefil curve is ± 9% at a level of confidence of 95% at any time during the filtration. [ABSTRACT FROM AUTHOR]

The results inferred from the present work show that Al3Ti phase has a strong affinity to react with silicon (Si) in the molten alloy leading to formation of (Al,Si)3Ti phase instead. This reaction is independent of the grain refiner type. The molten liquid temperature would change its morphology from platelets at 750°C into dendritic structure at 950°C. It has also been observed that (Al,Si)3Ti phase platelets precipitate within the α-aluminum dendrites, whereas TiB2 or AlB2 particles are released into the surrounding interdendritic regions. Introduction of the grain refiner, regardless its type, would cause change in the α-aluminum dendrite morphology from an elongated to a more rounded form. The results also reveal that addition of 100 ppm B will reduce the initial grain size by ∼85% which is more than the effect of addition of 0.2%Ti in the form of Al-10%Ti (about 65%). Elimination of undercooling is important to obtain the maximum grain refining effect. [ABSTRACT FROM AUTHOR]

The present study was performed on A356.2 alloy to explore the link between the effectiveness of different grain refiner practices and strontium (Sr) modification on both the eutectic silicon (Si) particle morphology and the final grain size. To achieve this objective, several types of grain refiners were added to the molten alloy at 750 °C in different concentrations and for various holding times. Strontium was added in the amount of 200 ppm. Thermal analysis combined with microstructure analysis using optical microscopy and electron probe microanalysis was used to assess the results. It was found that Sr has a certain affinity to react with the boron (B) in Al-5%Ti-1%B master alloy which partially reduced the grain refiner effectiveness. The eutectic Si particles maintained a similar degree of modification as in the non-grain refined Sr-modified condition. Al-4%B used with Sr led to the formation of a new intermetallic (SrB6), resulting in a significant decrease in the modification effect of Sr together with an increase in the obtained grain size. This effect increases at higher levels of added Al-4%B. The presence of excess Si leads to a change in the composition of the Al3Ti phase into (Al, Si)2Ti. [ABSTRACT FROM AUTHOR]

The present study is part of a larger study where the effectiveness of different types of grain refiners in strontium-modified hypoeutectic alloys was evaluated. Silicon was shown to affect the mechanism of nucleation of α-aluminum. To explore this phenomenon, an investigation was carried out on hypereutectic A390.1 alloy containing 17.3%Si to establish the role of primary silicon crystallization on subsequent α-aluminum and silicon eutectic reactions with different grain refiner additions. The alloy was modified with 0.02%Sr as before, and the same three-grain refiners: Al-10%Ti, Al-5%Ti-1%B, and Al-4%B master alloys, were used at controlled addition levels. The liquid metal was held at 750 °C for periods up to 120 min during which the molten metal was continuously stirred. The results show that addition of 0.1%Ti (using Al-10%Ti) to A390.1 alloy modified with 0.02%Sr results in reducing the initial grain size by about 20% only, due to transformation of Al3Ti phase to (Al,Si)2Ti phase which is a poor grain refiner. The stability of the (Al,Si)2Ti phase increases with the increase in the alloy Si content. The formation of (Al,Si)2Ti also reduces the undercooling caused by Sr addition, reducing the degree of morphology modification. Additionally, boron has a strong affinity to react with Sr, forming the compound SrB6, resulting in no grain refining or “poisoning,” regardless of the added amount of B or the holding time. Combined addition of Sr and B, however, improves the modification of the eutectic Si. In general, due to the high Si content of A390.1 alloy, it is difficult to achieve an appreciable degree of grain refining. [ABSTRACT FROM AUTHOR]

This study was conducted on Al–Cu–Mg and Al–Si–Cu–Mg alloys containing either 5%La or 5%Ce. Two levels of Ti addition were examined, i.e., 0.05% and 0.15%. Thermal analysis was the only technique used to obtain castings, from which samples were then sectioned for metallographic examination. Based on the results obtained, the following points may be highlighted. Addition of a fairly large amount of RE metals (La or Ce) leads to the appearance of several peaks in the solidification curve between the precipitation of the primary α-Al phase and the (Al–Al2Cu) eutectic reaction. Although a significant drop in the eutectic temperature is caused by the addition of 5%La or Ce, the corresponding modification of the eutectic Si is marginal. Two main types of intermetallics were documented: a gray phase in the form of sludge with a fixed composition and a white phase in the shape of thin platelets. Due to the high affinity of RE to react with Si, Fe, and Cu, several compositions were obtained explaining the observed multiple peaks in the solidification curve. Judging by the morphology of the gray phase, it is assumed that this phase is precipitated in the liquid state and acts as a nucleation site for the white phase. Lanthanum and Ce can substitute each other. [ABSTRACT FROM AUTHOR]

This study focused on investigating the effects of Sr-modification and solidification rate as well as the aging treatment conditions on the impact toughness behavior of Al-11%Si near-eutectic alloys with the objective of fully evaluating its behavior under high rates of loading. The Al-11%Si-based alloys, however, display lower impact energy values than those obtained for hypoeutectic 356 and 319 alloys. The impact behavior of aged Al-11%Si-based alloys is similar under both low and high solidification rate conditions; the air-cooled alloys (high solidification rate), however, display higher impact energy values than do furnace-cooled alloys (low solidification rate). Artificial aging at 240 °C for 44 h produces a significant improvement in the impact energy values as a result of softening effect, regardless of alloy composition. The presence of undissolved intermetallic phases, mainly AlCu and α-Al(Mn,Fe)Si, increases alloy brittleness and thus also reduces alloy toughness. The segregation of AlCu caused by Sr addition is a further parameter to be considered, especially for furnace-cooled alloys. The impact energy values of air-cooled alloys are significantly higher than those obtained for furnace-cooled alloys based on the microstructural differences between the two categories of alloys, regardless of alloy conditions. Crack propagation occurs mainly in the near-eutectic alloys by passing through the AlCu and/or α-iron intermetallic phases, shattering them into fragments. In numerous cases, the morphology of the intermetallic phase is retained, indicating that the fracture is of the transverse type rather than a particle/matrix fracture. [ABSTRACT FROM AUTHOR]

This study investigated the decomposition of π-AlMgFeSi into β-AlFeSi phase needles during extended periods of solution heat treatment and its effects on the mechanical properties of Al-7Si-0.55Mg-0.1Fe alloys. An analysis of the results obtained from the Charpy impact test using unnotched samples shows that the highest initiation and propagation energies are obtained for the as-cast and heat-treated alloys when these alloys are solidified at a high cooling rate and modified with strontium. An increase in the solution treatment time improves the impact properties of the alloys compared to the as-cast condition. In accordance with this finding, the recommended solution treatment time at which the maximum initiation and propagation energy values can be obtained is 20 h for all alloys studied. The results also show that the impact properties are more sensitive to the changes occurring in the microstructure which result from solution heat treatment and Sr modification, namely, the eutectic Si and π-phase morphologies, rather than those related to the tensile properties, i.e., to the Mg content in the matrix. Fracture analysis was carried out using a scanning electron microscope equipped with an EDX system for element analysis. The results obtained show that the tensile and impact fracture behavior of the Al-7Si-0.55Mg-0.1Fe alloys is controlled mainly by the morphology of the eutectic silicon. The π-phase iron intermetallics act as crack initiation sites and provide an easy path for crack propagation in both non-modified and Sr-modified alloys. The fracture analysis of the 80-h solution-treated sample shows the presence of newly formed β-phase needles which provide an additional source for crack initiation, and thus all the 80-h solution-treated alloys show the lowest energy values. [ABSTRACT FROM AUTHOR]

The present study was performed on 354 alloy containing Al-9% Si-1.8% Cu-0.5% Mg. Six alloys were prepared using 0.2 wt% Ti grain-refined 354 alloy, comprising alloy R (354 + 0.25% Zr) considered as the base or reference alloy, and five others, viz., alloys S (354 + 0.25% Zr + 2% Ni), T (354 + 0.25% Zr + 4% Ni), U (354 + 0.25% Zr + 0.75% Mn), V (354 + 0.25% Zr + 0.75% Mn + 2% Ni), and Z (354 + 0.25% Zr + 0.15% Sc). The tensile data showed that the UTS and percent elongation values of R, S, T, U, V and Z alloys increased in the one-step solution heat-treated (SHT 1) condition compared to the as-cast case. The multi-step solution heat treatment (SHT 2) displayed higher tensile properties than those achieved with SHT 1 treatment. The use of the T62 treatment, incorporating the SHT 2, allows for maximum dissolution of the copper phases in the multiple stages of solution treatment, resulting in the greatest improvement in both UTS and YS. Without stabilization, T6 and T62 treatments provide the best improvements in both UTS and YS values of all alloys. The best tensile properties of alloys tested at room temperature after stabilization at 250 °C for 200 h are obtained with the T6 heat treatment. After T62 treatment, Alloy U showed the maximum increase in UTS and YS values. Addition of Zr, Ni, Mn and Sc to 354 alloys improves the high temperature tensile properties. Alloys S and U perform better when tested under high temperature conditions, after one hour stabilization at 250 °C. After 200 h stabilization at 250 °C, however, the strength of the T6-treated alloys is reduced considerably, while the ductility is increased, with alloy R showing the highest percent elongation, ~ 19%, which is attributed to the precipitation of a high density of coarse Al 2 Cu phase particles during the prolonged stabilization treatment at 250 °C. [ABSTRACT FROM AUTHOR]

A correction is presented to the article "Parameters Controlling the Impact Toughness of A356.2 Cast Alloy" which was published in previous issue of the periodical.

The present work was performed on an A319.2 alloy with different amounts of Fe. The melt was poured from two temperatures, i.e. 750 and 950 °C. The results show that increasing the melt superheat leads to an increase in the undercooling, e.g., 1.2 and 3 °C for melt temperatures of 750 and 950 °C, respectively. The presence of oxide films accelerates the precipitation of the β-AlFeSi iron intermetallic phase platelets. The amount of oxide films increases with the increase in the melt temperature, coupled with the addition of Sr and P. Strontium has a strong tendency to break down the length of the β-platelets, e.g., 160 and 109 µm, for non-modified and Sr-modified alloys containing 1.2% Fe, respectively. In the absence of Sr and for a melt temperature of ~950 °C, P precipitates in the form of (Al, P)O oxide films. These films act as nucleation sites for the precipitation of β-platelets much finer (60 µm) than those obtained for samples poured at 750 °C. The addition of P to the 319 alloy modified with Sr results in the precipitation of (Al, P, Sr)O, which significantly reduces the beneficial effect of Sr. Titanium precipitates in the form of Ti(Al, Si) platelets at 740 °C. Relatively fine β-platelets (~130 µm) can precipitate along the long sides of the Ti-rich platelets. Iron has a harmful effect on the alloy strength due to the precipitation of dense β-platelets. The addition of Sr improves the alloy mechanical properties through fragmentation of β-platelets, especially at low content of Fe. Finally, phosphorus has an abnormal effect on the three tensile parameters, and the Sr-P interaction diminishes the beneficial effect of Sr. [ABSTRACT FROM AUTHOR]

The aim of the present study has been to investigate the metallurgical parameters controlling the microstructural evolution and porosity formation in Al-Si-Mg and Al-Si-Cu alloys, through a study of the microstructural characteristics of directionally solidified A356 and 319 type alloys as a function of iron content, Sr addition (~250 ppm), and solidification rate. In the Sr-modified alloys, porosity formation is frequently associated with strontium oxides (particles or films), as well as β-AlFeSi phase platelets. These oxides (with a stoichiometric composition close to AlSrO) are formed during melting, due to the high oxygen affinity of strontium, and are difficult to remove via degassing. The pore morphology (round or irregular) is determined by the form of the oxide, i.e. fine dispersed particles or thick films. Round pores are also observed surrounded by Al-Si eutectic regions. Aluminum oxide films trapped in the molten metal lead to the formation of coarser and deeper pores than those formed due to the strontium oxides. These pores can also link with each other and are characterized by the presence of solidified metal trapped within the aluminum oxide films, close to the periphery. The form of these pores is controlled by the amount of gases trapped within the pores during solidification. [ABSTRACT FROM AUTHOR]

A study was carried out to investigate the effects of iron content, porosity and solidification rate on the impact properties and fracture behavior of A356.2-type alloys. The results show that impact properties improve with increase in solidification rate and decrease in Fe content. Unmodified A356.2 alloys show linear correlations, while modified A356.2 alloys show logarithmic correlations at all solidification rates ( R > 0.95 in all cases). Impact properties obtained at the highest solidification rate are far superior to those obtained at other solidification rates. The β-AlFeSi intermetallic deteriorates impact properties significantly, the effect being most apparent within 10-50 μm β-platelet sizes in A356.2 alloy. Fairly good correlations between porosity and impact properties are obtained. Strontium is effective in improving impact energy, even at high Fe levels. A good inverse relation is obtained between average crack speed and impact energy, highest crack speeds being observed in unmodified samples obtained at highest Fe contents and lowest solidification rates. Impact testing is sensitive to variations in microstructure or casting defects. Impact energy-strength plots show exponential relationships, whereas impact energy-ductility plots display linear relationships for all alloys, modified or not, regardless of the alloy composition. In A356.2 alloys, cracks initiate mainly through the fracture of Si particles or their debonding from the Al matrix, while crack propagation occurs through the coalescence of fractured Si particles, except when β-AlFeSi platelets are present, in which case the latter take precedence. [ABSTRACT FROM AUTHOR]

The present study was performed on A356 alloy with the main aim of investigating the effects of La and Ce additions to 356 alloys (with and without 100 ppm Sr) on the microstructure and porosity formation in these alloys. Measured amounts of La, Ce, and Sr were added to the molten alloy. The results showed that, in the absence of Sr, addition of La and Ce leads to an increase in the nucleation temperature of the α-Al dendritic network with a decrease in the temperature of the eutectic Si precipitation, resulting in increasing the freezing range. Addition of 100 ppm Sr results in neutralizing these effects. The presence of La or Ce in the casting has a minor effect on eutectic Si modification, in spite of the observed depression in the eutectic temperature. It should be noted that Ce is more effective than La as an alternate modifying agent. According to the atomic radius ratio, rLa/rSi is 1.604 and rCe/rSi is 1.559, theoretically, which shows that Ce is relatively more effective than La. The present findings confirm that Sr is the most dominating modification agent. Interaction between rare earth (RE) metals and Sr would reduce the effectiveness of Sr. Although modification with Sr causes the formation of shrinkage porosity, it also reacts with RE-rich intermetallics, resulting in their fragmentation. [ABSTRACT FROM AUTHOR]

The present work was performed on A413.1 alloy containing 0.2–1.5 wt% rare earth metals (lanthanum or cerium), 0.05–0.15% Ti, and 0–0.02 wt% Sr. These elements were either added individually or combined. Thermal analysis, image analysis, and electron probe microanalysis were the main techniques employed in the present study. The results show that the use of the depression in the eutectic temperature as a function of alloy modification cannot be applied in the case when the alloy is treated with rare earth metals. Increasing the concentration of RE increases the solidification zone especially in Sr-modified alloys leading to poor feeding ability. This observation is more prominent in the case of Ce addition. Depending upon the amount of added Ti, two RE based intermetallics can be formed: (i) a white phase, mainly platelet-like (approximately 2.5 μm thick), that is rich in RE, Si, Cu, and Al and (ii) a second phase made up of mainly grey sludge particles (star-like) branching in different directions. The grey phase is rich in Ti with some RE (almost 20% of that in the white phase) with traces of Si and Cu. There is a strong interaction between RE and Sr leading to a reduction in the efficiency of Sr as a eutectic Si modifier causing particle demodification. [ABSTRACT FROM AUTHOR]

The present study was performed on 356 and 413 alloys containing various amounts of hydrogen (H), titanium diboride (TiB) and strontium (Sr). The results show that the eutectic silicon particles in non-modified alloys undergo coarsening during the solutionizing treatment. A new mechanism, based on the Ostwald theory, has been proposed to explain the observed phenomenon. Although the variation in melt treatment parameters has no significant influence on the alloy hardness, it does have a great effect on the alloy impact toughness. Best results are obtained when the alloy is degassed, Sr-modified and grain refined. Also, Sr-modified, degassed 413 alloys have been found to possess good impact toughness. Precipitation of MgSi phase particles in 356 alloy is more effective as a hardening agent than the AlCu phase precipitated in the 413 alloy. The increased Si content in non-modified 413 alloys accelerates crack initiation and propagation, leading to low toughness values. Modifying the 413 alloys with 200 ppm Sr results in a more even distribution of the spheroidized eutectic Si particles and hence improves the alloy toughness. [ABSTRACT FROM AUTHOR]

The present study was carried out on a 380 alloy containing 9.13% Si, 3.22% Cu, 1.01% Fe, 0.06% Mg, 0.16% Mn, and 2.28% Zn. The magnesium level was increased to 0.3 and 0.55%, by adding pure Mg to the melt. Tensile and fatigue samples were produced using low pressure die casting. The results show that the average dendrite arm spacing was about 6 μm. Increasing the amount of Mg from 0.06% to 0.55% increased the volume fraction of π-Al8Mg3FeSi6 and Q-Al5Cu2Mg8Si6 phases from 0.8% to 1.7%. Following solutionizing at 490°C for 8 h, the maximum ultimate tensile strength was obtained from alloys containing 0.3% Mg. Further increases in Mg content resulted in an increase in the amount of insoluble intermetallics and, hence, low tensile strength. Aging at 155°C for times up to 25 h resulted in a linear increase in the alloy strength regardless of the amount of added Mg. Aging at 220°C, however, revealed multiple peaks corresponding to the precipitation of various phases. A good relation between the applied force and the number of cycles prior to failure was established. The alloy containing 0.3% Mg produced the best fatigue resistance. The effect of porosity was more pronounced on the fatigue samples than on the tensile bars. [ABSTRACT FROM AUTHOR]

The present study was performed on 356 and 413 alloys containing various amounts of hydrogen (H 2 ), titanium diboride (TiB 2 ), and strontium (Sr). The results show that the eutectic silicon particles in non-modified alloys undergo coarsening during the solutionizing treatment. High energy levels are obtained when the alloy is degassed, Sr-modified, and grain refined. Precipitation of Mg 2 Si phase particles in 356 alloys is more effective as a hardening agent than the Al 2 Cu phase precipitated in the 413 alloy which contributes to the alloy strength/hardness. The increased Si content in non-modified 413 alloys accelerates crack initiation and propagation, leading to low toughness values. Modifying the 413 alloys with 200 ppm Sr results in a more even distribution of the spheroidized eutectic Si particles and hence better the alloy toughness. Exceeding the required amount of Ti-containing grain refiner may result in the introduction of a large amount of brittle Al 3 Ti platelets that would reduce the alloy toughness. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effect of Cu addition on the occurrence of incipient melting. [•] Role of solution heat treatment in controlling the tensile properties of Al–Si–Cu cast alloys. [•] Phase identification using WDS analysis. [•] Effect of Mg addition on the alloy performance. [Copyright &y& Elsevier]

Abstract: Castings were prepared from 319.2 alloy melts, containing Fe levels of 0.2–1.0 wt%. Sr-modified (∼200 ppm) melts were also prepared for each alloy Fe level. The end-chilled refractory mold used provided directional solidification and a range of cooling rates (or dendrite arm spacings, DAS) within the same casting. Impact test samples were machined from specimen blanks sectioned from the castings at various heights above the chill end provided DASs of 23–85μm. All samples were T6-heat-treated before testing keeping with Aluminum Association recommendations. The results show that at low Fe levels and high cooling rates (0.4% Fe, 23 μm DAS), crack initiation and propagation in unmodified 319 alloys occurs through the cleavage of β-Al5FeSi platelets (rather than by their decohesion from the matrix). The morphology and the size of the platelets (individual or branched) are important in determining the direction of crack propagation. Increasing the DAS to 83μm leads to cleavage fracture. In this case, the fracture path follows a transgranular plane that is usually a well-defined crystallographic plane as judged by the relatively large smooth surfaces of the β-Al5FeSi phase platelets. Cracks also propagate through the fracture of undissolved CuAl2 or other Cu-intermetallics, as well as through fragmented Si particles. In Sr-modified 319 alloys, cracks are mostly initiated by the fragmentation or cleavage of perforated β-phase platelets, in addition to that of coarse Si particles and undissolved Cu-intermetallics.The amount of undissolved Cu- intermetallics is directly related to the applied cooling rate. Slow cooling rate (DAS ≈83µm) results in the precipitation of Cu- containing phases on the β-platelets, amplifying the likehood for crack propagation through these loacations. [Copyright &y& Elsevier]

Abstract: The present study aims to investigate the influence of the addition of Ti and B in the form of five different grain refiners/aluminium master alloys (Al–10%Ti, Al–5%Ti–1%B, Al–2.5%Ti–2.5%B, Al–1.7%Ti–1.4%B and Al–4%B) in conjunction with that of Sr (as modifier) added in the form of Al–10%Sr master alloy to A356.2 alloy. Grain refinement of an A356.2 alloy with Ti and B additions in the ranges of 0.02–0.5% and 0.01–0.5%, respectively, was examined using these different types of grain refiners. Strontium additions of 30 and 200 ppm were made. All alloys were T6-heat treated before mechanical testing. Tensile and impact tests were conducted to evaluate the influence of the interaction between grain refiner and modifier on the mechanical properties. The properties were determined for both the as-cast and heat-treated conditions. [Copyright &y& Elsevier]

The present work was performed on experimental Al–Si near eutectic cast alloys, with different additives mainly Fe, Mg, Mn, Cr, Sr and P. The alloys were cooled at 0·8°C s−1, very close to equilibrium conditions. Precipitated phases, primarily Fe, Cu, Mg and Sr based intermetallics, were examined. Although the phases reported in the present work were documented previously, the range of chemical composition of each phase was confirmed using an electron probe microanalyser equipped with wavelength dispersive spectroscopy and electron dispersive X-ray spectroscopy facilities. [ABSTRACT FROM AUTHOR]