Search

The softening of the heat affected zone (HAZ) remains a significant challenge in fusion welding of novel Al–Mg–Si–Cu alloy, and the underlying mechanisms vary across different aging states. However, limited research has been conducted on this topic. Therefore, this study investigates the influence of various aging states on the microstructure and mechanical properties within the HAZ of welded joints by selecting extrusions treated with T4, T5, and T6 heat treatments. The results indicate that the increase in hardness of HAZ I is attributed to solid solution strengthening. In the HAZ I, the precipitated phases are mostly dissolved into the matrix under the influence of a peak temperature of 464.6 °C, and no residual precipitated phase is detected in T4 and T5 alloy joints, while some undissolved Q phase is observed in T6 alloy joint. The decrease in hardness of HAZ Ⅱ is attributed to the limited precipitation of coarse β'' and Q' phases for the T4 alloy welded joints, which weakens the solid solution strengthening. However, the softening mechanisms in the HAZ Ⅱ of the T5 and T6 alloy joints are ascribed to the dissolution of β'' and subsequent precipitation of Q' and Q phases. HAZ Ⅲ, close to the base metal, exhibits a lesser degree of influence and thus experiences a gradual recovery in hardness. This study can provide theoretical guidance for the exploration of high-strength, heat-resistant aluminum alloys.

In this study, the tensile creep behavior of a hot-rolled Mg-4Y-3.5Nd alloy subjected to different prior thermo-mechanical treatments was investigated at 220 ℃. Five groups of samples were prepared using different combinations of the solid solution (S), aging treatment at 220 ℃ for 30 h (A), and hot compression at 490 ℃ to a true strain of 0.25 (C). The abbreviations for the samples are S, SA, SC, SAC, and SCA. Upon examining the yield strength and creep resistance, it was found that creep resistance could not be directly predicted by the yield strength. The stability of the deformation bands (DBs) induced by prior thermo-mechanical treatment plays an important role in determining the creep resistance. The dislocation of the DBs and demonstrated the best creep resistance in the SAC sample, which were prepared using a solid solution, aging treatment, and subsequent hot compression. However, despite the highest yield strength, frequent dislocation motions destroyed the stability of the DBs and deteriorated the creep resistance of the SCA sample, which were prepared using a solid solution, hot compression, and subsequent aging treatment. Among the thermo-mechanical treatments used in this study, the application of aging treatment was important to obtain the resultant creep resistance. When the aging treatment was performed prior to hot compression, the creep resistance could be further enhanced based only on hot compression. Accordingly, the sequence from the strongest to the weakest creep resistance was SAC > SC > S > SCA > SA.

In this work, the bending behavior of high-strength Al–Mg–Si–Cu alloys and AA6061 under different artificial aging condition was investigated. The existing springback prediction formula is suitable for commercial AA6061 alloy, but not for high-strength Al–Mg–Si–Cu alloy. Subsequently, the microstructure, mechanical properties and residual stress of AA6061 and high-strength Al– Mg–Si–Cu alloys were investigated. The results show that the yield strength and residual stress play important roles on the springback of high-strength Al–Mg–Si–Cu alloy. In addition, a springback prediction formula based on residual tensile stress has been proposed, which makes the prediction accuracy higher than 96 %. This provides theoretical guidance and data support for the application of high-strength Al–Mg–Si–Cu alloys in lightweight automotive materials.

The process of symmetrical multidirectional pressure was adopted to inhibit the macrosegregation of eutectic Si in squeeze cast A356 alloy. Five pressure modes were applied to study the effects of multidirectional pressure and the timing of pressure application on the macrosegregation of eutectic Si. The results show that the directional movement of the solute-rich liquid phase could be inhibited by symmetrical multidirectional pressure. Therefore, the macrosegregation of eutectic Si in the casting part was inhibited. Moreover, the timing of pressure application should be matched with the local pressure position. After the effective inhibition of the macrosegregation of eutectic Si, the elongation of the alloy was significantly improved, reaching up to 7.12%. In addition, the plastic deformation region was observed at the local pressure position. The grains in the plastic deformation region were refined. The proportion of low-angle grain boundaries in the deformed region was about 30%, which was much higher than that in the other undeformed region. The size of the Fe-containing intermetallics in the deformed region decreased to 5–10 μm, which is favorable for the mechanical properties of the alloy.

Improvement of corrosion resistance in high-strength Al–Si–Cu–Mg casting alloy is an important issue for its application in humid and corrosion environment. In this paper, the effect of Cr on microstructure, mechanical properties and corrosion behavior of Al–9Si-1.2Cu-0.5 Mg alloy were investigated. The results indicate that 0.052 % and 0.106 % Cr addition shows a slight strengthening for mechanical properties by introducing AlSiFeCr dispersoids, 0.052 % Cr addition effectively enhances the corrosion resistance of the alloy. The addition of 0.052%Cr not only increase the thickness and stability of the passive film, but also has an obvious effect on the charge transfer process. 0.052 % Cr addition reduces the potential difference between cathode phases and Al matrix. The results of first-principles calculations indicate that the (001) surface of CrO2 would have an effect of adsorbing Cl− ions in the passive film/solution interface, the interaction between Cl and neighboring Cr atoms implies the formation of chemical bonds between Cl atoms and the surrounding Cr atoms at adsorption sites. It contributes to weaken the attack of the passive film by Cl− ions. When Cr level increases to 0.106 %, the appearance of AlSiFeCr dispersoids may result in the additional electrochemical process and weaken the protection on the matrix. This paper designs a novel Al–Si–Cu–Mg–Cr casting alloy with high mechanical properties and high corrosion resistance, expanding automotive industry application of casting aluminum alloy.

Graphene has recently garnered significant attention as an exceptional nanofiller for aluminum (Al) matrix composites due to its remarkable mechanical strength, elevated thermal and electrical conductivities. For practical industrial applications, it is necessary to develop large-scale production technology. To this end, we have utilized a scalable stir-casting process to fabricate graphene-reinforced aluminum matrix composites. The microstructure, mechanical properties, electrical and thermal conductivities of the composites with varying graphene contents were characterized. Through testing, it was confirmed that graphene remained intact within the aluminum matrix during the stir-casting process, and the damage to the graphene sheet during the fabrication of composites was slight. High-resolution microscopic observation shows that aluminum, graphene and aluminum carbide co-exist within the composites. Compared to its pure aluminum counterpart, the Vickers hardness of the optimal composite sample (with a graphene content of 0.2 wt.%) exhibits a significant increase of 42%. Also, this superior composite sample exhibits a remarkable increase of 5% and 38% in its electrical and thermal conductivities respectively. The performance evolution and improvement mechanisms have been thoroughly investigated and revealed. The test results suggest that preformed blocks and stir casting are promising technologies for the large-scale production of graphene-aluminum composites.

The intermediate temperature deformation behavior and microstructural evolution of a spray formed 7075 Al alloy were performed at temperatures 60–120 °C with strain rates 0.00001–0.1 s−1. The results reveal that the softening mechanism of the intermediate temperature deformation is dynamic recovery (DRV), which can be quantitated by Zener-Hollomon (Z) parameter. The constitutive equation can reasonably predict the stress-strain behavior of the alloy at intermediate temperatures. The activation energy is related to the deformation process and the interactions of the substructure, the average value is 140.1 kJ/mol. The higher efficiency of power dissipation in the processing map is related to the DRV at lower deformation temperatures. The optimum processing domain is located at the temperature of 90–120 °C and strain rate of 0.006–0.1 s−1 with a power dissipation efficiency range of 20%–40%. The processing parameters of the intermediate temperature deformation should be strictly controlled according to the strain. The uniform microstructure of 7075 alloys obtained by spray forming is crucial to overcome the disadvantage of poor deformability. The inferior coordinated deformation facilitates crack propagation at low strain rates. The high-density dislocation provides adequate nucleation sites for dynamic precipitation. The level of dynamic restoration facilitates the transformation from low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs). The dislocations move to the grain/sub-grain boundary to form dislocation walls at low temperatures. The contribution to the stress from grain boundary (13.2–17.7 MPa), nanoscale precipitates (65.7–191.5 MPa), and dislocation (5.9–23.4 MPa) increases the difficulty of deformation. The deformation process at higher temperatures (105–120 °C) can be facilitated by the dissolution and coarsening of the nanoscale precipitates, and dislocation motion at the grain boundary.

The influence of thermophysical properties of materials on the porosity and microstructure of dissimilar lap joints between laser-welded Al–Si–Mg cast and Al–Mg–Si–Cu wrought aluminum alloys was investigated. The low thermal conductivity and viscosity of the weld would promote bubble escape, while the high electrical conductivity of the base material would increase the melt depth and reduce the convection intensity in the melt pool, thus increasing the difficulty of bubble escape. The variation in thermophysical properties did not significantly impact the distribution of elements, the type of precipitated phases, and the dislocation density, however, it did affect grain morphology. Differences in thermal diffusion coefficients between base materials created conditions for constitutional supercooling, increasing the likelihood of a columnar-to-equiaxed transition. Moreover, the temperature difference between the liquid phase lines of the weld and base materials facilitated the liquid base material flushed into the weld to solidify before mixing, resulting in an “island” formation. This “island” acted as a heterogeneous nucleation site, leading to equiaxed grain layer formation in the lowest zone of the weld. The variations in thermophysical properties exerted an influence on the tensile strength by impacting both the melt depth and the grain morphology of the weld but did not yield a significant impact on the average microhardness.

The 2319-Al alloy is widely used in aviation industry. The crack-free 2319 alloy thin-walled sample was fabricated utilizing the laser-CMT composite additive manufacturing technique, achieving a material utilization rate of 96.43%. The impact of deposition parameters and deposition height on the microstructure and mechanical properties was studied. The microhardness of the additive manufacturing samples exhibited a gradual decrease from construction direction, with values reaching 90 HV, 78 HV, and 72 HV, respectively. The tensile property also exhibited a gradual decrease from the bottom to the top; the highest tensile strength was 296 MPa. The grain size along the construction direction of the deposited sample gradually increased, exhibiting respective sizes of 34.7 um, 36.6 um, and 45.7 um. With the increase in the height of the second phase, the segregation at the grain boundary is intensified, and as the size inside the grain increases, the corresponding density decreases. The good laser-CMT composite additively manufactured 2319 aluminum alloy samples could be obtained under the optimized deposition parameters.

In this work, creep behaviors of dilute Mg–Mn–Zn alloys were investigated in extruded rods (ER) with bimodal grain microstructures and extruded sheets (ES) with homogeneous microstructures. Tensile creep tests were carried out at 423 K along the extrusion direction (ED) and transverse direction (TD). For brevity, the samples were named as ER-ED, ER-TD, ES-ED and ES-TD, respectively. All samples' creep is dominated by dislocation movement, and different types of dislocation slip are seen in the different samples under loading along each direction. For the ER sample, the creep mechanisms of the ER-ED sample were determined to be cross-slip accompanied by pyramidal slip. Differently, the creep of the ER-TD sample was dominated by basal slip and accompanied by grain boundary bulging, which induced the worst creep resistance. For the ES alloy, the creep mechanisms were pyramidal and cross-slip, but the cross-slip density of the ES-ED sample was higher. Accordingly, the creep test results indicated that the creep resistance was ranked in an order of ES-TD/ED > ER-ED » ER-TD. Furthermore, bimodal grain microstructure accelerates creep at a similar texture effect level, where grain boundary bulging was clearly observed, as well as the decreased KAM and increased fraction of M/HABs (middle-to-high angle boundaries). These typical softening characteristics might be responsible for weakening the ER-ED sample from the highest room-temperature yield strength to the inferior creep resistance to ES-TD/ED samples, meaning the thermal instability of this strong heterogeneous microstructure.

Understanding the evolution of Fe–containing intermetallic compounds (Fe–IMCs) in Al–Si–Mg alloys is essential for improving the mechanical performances. This paper aims to systemically evaluate the influences of both the single addition of Mn or Mo, and the combined additions of Mn and Mo on the evolution of Fe–IMCs and mechanical performances of Al–Si–Mg cast alloys. Results reveal that the as–cast microstructures of these alloys are primarily composed of Al3M (M means Ti, Zr, or TiZr), α–Al, eutectic Si, Mg2Si, Q–Al5Cu2Mg8Si6, and some irregular Fe–IMCs. It is clear that the morphology and size of Fe–IMCs are significantly affected by the single or combined addition of Mn and Mo. Moderate Mn content facilitates the formation of Chinese script–like α–Al(FeMn)Si phases that are favorable to the mechanical properties. The combined addition of Mn and Mo refines the α–Al(FeMn)Si phases and promotes the formation of Chinese script–like α–Al(FeMnMo)Si phases. Furthermore, as the Mo level increases, β–AlFeSi, π–Al8FeMg3Si6, and α–Al(FeMn)Si disappear successively, which also helps improve the mechanical performances. In this article, maximum hardness, ultimate tensile strength, yield strength and elongation of 87.04 HV, 275.34 MPa, 139.70 MPa, 7.88% are obtained when Fe, Mn and Mo are added at 0.20wt.%, 0.02wt.%, and 0.27wt.%, respectively. The purpose of this work is to provide an efficient method to minimize or even eliminate the adverse effects of Fe–IMCs and thus improve the mechanical performances of Al–Si–Mg cast alloys.

In this paper, the melt turbulence process was introduced to result in Fe-containing particle agglomeration and achieve highly efficient Fe separation in Al-Si alloy melt. Microstructure analysis, 3D-morphology extraction, X-ray microscopy (μCT) analysis were conducted to discuss the phenomenon and mechanism of Fe-containing particle agglomeration. The experimental results indicate that the Fe-containing particle is suitable for separation due to the high precipitation temperature and particulate morphology. Then, the intervention of rotor stirring greatly promotes collision, adhesion and agglomeration of Fe-containing particles during sedimentation separation. The Fe-containing particle agglomeration showed a maximum diameter of 1650 μm and a 67.67% reduction of Fe were obtained after rotor stirring. When the sedimentation separation is intervened by rotor stirring and argon blowing, the agglomeration effect of Fe-containing particles further promotes. The Fe-containing particle agglomeration shows the maximum size of 1800 μm and a high Fe separation efficiency of 74.46% were obtained. The simultaneously exerting of rotor stirring and argon blowing promotes the formation of agglomeration attached by small Fe-containing particles, which also contributes to higher Fe separation efficiency. These results provided a new sight to achieve high Fe separation efficiency in Al-Si alloy melt by industrially viable methods.

In this paper, we investigated the influence of calcium (Ca) on the electrochemical and corrosion properties of Al–Mg–Sn–Ga alloys in neutral and alkaline electrolytes, respectively. Results indicate that Ca element promotes the uniform dissolution of the anode and improve its discharge efficiency. The peak energy densities of the Al-0.5Mg-0.1Sn-0.05Ga-0.1Ca alloy in neutral and alkaline solutions are 3361 and 3581 Wh kg−1, respectively. Compared with calcium-free alloy, the increase is 5.3% and 26.5%, respectively. Additionally, the severe intergranular corrosion behavior of Al-0.5Mg-0.1Sn-0.05Ga alloy can be significantly inhibited by adding Ca element under alkaline conditions. Therefore, the addition of Ca element further optimizes the discharge performance of Al–Mg–Sn–Ga-based anodes and enhances its environmental adaptability.

Dissimilar-filler welding is widely used for joining aluminum components. However, macrosegregation that will degrade the performance of the weld joint commonly occurs within the weld metal, because of the compositional difference between the filler and base metals. This study reports a new mechanism for the macrosegregation introduction during dissimilar-filler welding. Liquid segregation is induced in the weld pool owing to dynamic heterogeneous mixing between the filler and the base metal melts. In the front portion of the weld pool, heterogeneous mixing proceeds uninhibited owing to convection and the presence of a continuous heat source. However, away from this region, the temperature of the weld pool is significantly reduced, and solidification dominates heterogeneous mixing. If the heterogeneous mixing has none or only partially occurred, this liquid segregation is frozen into the weld metal to introduce macrosegregation. The mechanism elucidation will provide new insights into the improvement of weld joints.

A comprehensive understanding of the structural characteristics and mechanical behavior of Fe-containing phases is important for high-Fe-level Al-Si alloys. In this paper, the crystal characteristics, thermal stability, thermophysical properties and mechanical behavior of multicomponent α-AlFeMnSi and α-AlFeMnCrSi phases are investigated by experimental studies and first-principles calculations. The results indicate that it is easier for Fe and Cr to substitute the Mn-12j site in α-AlMnSi in thermodynamics; Cr is preferred to Fe for substituting Mn-12j/k sites due to its lower formation enthalpy after single substitutions at Mn atom sites. The α-AlFeMnCrSi phase shows higher thermal stability, modulus and intrinsic hardness and a lower volumetric thermal expansion coefficient at different temperatures due to the strong chemical bonding of Si-Fe and Si-Cr. Moreover, the α-AlFeMnCrSi phase has a higher ideal strength (10.65 GPa) and lower stacking fault energy (1.10 × 103 mJ/m2). The stacking fault energy evolution of the different Fe-containing phases is mainly attributed to the differential charge-density redistribution. The strong chemical bonds of Si-Fe, Si-Mn and Si-Cr are important factors affecting the thermophysical and mechanical behaviors of the α-AlFeMnCrSi phase.

The effect of cold pre-deformation combined with ageing treatment on age hardening behavior and associated intergranular corrosion (IGC) resistance of an Zn-bearing 5xxx aluminum alloy is investigated in this study. Results reveal that the strength of the alloy is improved greatly by the prior cold deformation basing on the synergistic effect of work hardening and ageing strengthening. With the combination of cold pre-deformation and ageing treatment, the peak yield strength of the alloy is 314.7 MPa, which increases by 110% than that of the T6 treated alloy. Moreover, the intergranular microstructure such as grain boundary precipitates can be optimized by coordinating the pre-deformation and ageing treatment. Hence, Al–Mg–Zn alloy with high strength and excellent IGC resistance can be obtained by combining the prior cold deformation and ageing treatment.

Fine, uniform and equiaxed grain structure is one of the most striking features of high-quality Al targets. In general, the imposition of magnetic stirring on the liquid Al during the solidification process is an effective method to promote grain refinement. In the present study, a self–made rotating system of permanent magnets is reported to stir liquid Al during solidification. The temperature change and grain structure of pure Al subjected to a permanent magnet stirring (PMS) are analyzed. The experimental results reveal that the forced convection driven by PMS can lead to a more homogeneous temperature field in the melt. Meanwhile, PMS can greatly refine the grain structure of pure Al and eliminate cavities, but it may induce more gas holes in the ingots. Moreover, a fresh intermittent permanent magnet stirring (I-PMS) approach has been proposed and successfully applied to realize grain refinement of pure Al. Some casting problems can be perfectly solved using suitable processing parameters. Through some valuable experimental works, systematic researches on grain refinement of pure Al under PMS are performed to better understand its refining mechanisms. Therefore, this article further enhances our understanding of related fields and fills the research blank.

A novel technology, termed intermittent permanent magnet stirring (I-PMS), is proposed to improve the quality of aluminum alloy ingots. In this paper, the melt flow and solidification structure of Al–4.5Cu alloy were investigated through I-PMS. The grain refinement mechanism of I-PMS is also discussed. The results indicate that the melt flow patterns and distributions can be greatly affected by I-PMS. When I-PMS is applied during solidification, the melt undergoes a series of complicated periodic three-dimensional flows. Compared without I-PMS, the solidification structure of Al–4.5Cu alloy with I-PMS was remarkably refined, and the optimum solidification structure could be realized utilizing appropriate processing parameters.

This work investigated the relationship between the morphology of AlFeSi intermetallics compounds (IMCs) and grains, and its influence on the corrosion behavior of the surface of Al–Mg–Si alloy laser welds. Due to the segregation of solute elements on the grain boundary, coarse AlFeSi IMCs were more likely to precipitate along the grain boundary. As a result, the “linear-like” AlFeSi IMCs was only found along the straight grain boundary of columnar grains, leading to the deterioration of corrosion resistance, but for the equiaxed grains, only small rod-like AlFeSi IMCs was along the grain boundary. Compared to the small rod-like AlFeSi IMCs at GBs of equiaxed grains, the “linear-like” AlFeSi IMCs at the straight GBs of columnar grains increased the interface area between α-Al, leading to a more evident intergranular corrosion at columnar boundary.

Nanoscale α-Al(FeMn)Si dispersoids in Al alloys play a vital role in improving the recrystallization resistance and mechanical properties of alloys at elevated temperatures. This study investigates the influence of Cu on the precipitation behavior of α-dispersoids in Al–Mg–Si alloys during heat treatment at 500 °C. α-dispersoids in an alloy without Cu addition had rod- or plate-like morphologies. The addition of Cu effectively inhibits the precipitation of α-dispersoids through the formation of fine spherical dispersoids, resulting enhanced mechanical properties of the alloy at elevated temperatures. Evidence from high-resolution transmission electron microscopy demonstrated that the rod- or plate-like structures have simple cubic structures, whereas the spherical α-dispersoids are coherent with the Al matrix along the [101] zone axis of Al, resulting in finer dispersoids, higher thermal stability, and lower coarsening rates. However, its crystal structure requires further investigation.

The solute mixing phenomena of filler and base metal melts during dissimilar-filler metal-inert gas (MIG) welding are simulated by a multi-phase lattice Boltzmann (LB) model for predicting macrosegregation formation in the weld joint. The LB models incorporates the calculations of fluid field and solute transport, and the quantitative capalibity is validated through the problem of one-dimensional liquid diffusion. For the MIG welding of AA6063 sheets with an ER5183 filler wire, the simulation results reveal that the periodic impingement of heterogeneous filler metal droplets leads to symmetrical vortex flows accompanied by the unmixed zones formed in the center. These unmixed zones locate in the bulk weld pool and would develop into macrosegregation in the weld joint. In addition, the fluid flow near the fusion boundary remains almost stagnant, which gives rise to the appearance of the thereby continuous unmixed zone. The predicted distribution of unmixed zone in the weld pool agree well with the macrosegregation patterns in the weld joint observed in the experiments. For partially mimicking the effect of external magnetic field on droplet movement recorded by a high-speed camera, random droplet flight directions are arranged in the LB simulations. With the increase of droplet impact speed (Weber number) and the arrangement of random droplet flight direction, the simulated Mg concentration in the weld pool becomes more uniform, implying that the risk of macrosegregation formation is reduced. The LB simulations provides insight for better understanding the formation of weld defects during MIG welding with a dissimilar filler metal.

This work investigated the transformation of Fe-bearing intermetallics and its influence on the corrosion behavior of Al–Mg–Si alloy weld joints. The results showed that the size and type of Fe-bearing intermetallics determined the pitting corrosion resistance of weldment regions. The partially melted zone (PMZ) suffered most serious corrosion attack, because of the formation of coarse needle-like β-AlFeSi. The heat-affected zone (HAZ) immediately behind the PMZ (HAZ-Ⅰ) experienced a complete transformation of β-AlFeSi into α-AlFeSi, but in the rest of the HAZ (HAZ-Ⅱ) was not sufficient for this transformation. Therefore, the HAZ-Ⅰ was more resistant to pitting corrosion than HAZ-Ⅱ.

In situ Mg2Si particles often show coarse and irregular morphologies in Al–matrix composites, which results in inhomogeneous microstructures and poor mechanical properties. This leads to poor deformation ability in Mg2Si particles reinforced Al–matrix composites. Herein, a refined process exploiting refined Mg2Si particles was developed to enhance microstructure homogeneity after hot rolling in an Al-11.73%Mg-6.63%Si composite. The hot-rolled sheet reduces the macroscopic cracking on the edge when the Mg2Si particles of the as-cast microstructure are refined by the addition of phosphorus. The refined Mg2Si particles in the as-cast state shows further size reduction and exhibits homogeneous distribution by hot rolling (reduction of 76%). The microstructure also shows uniform deformation zones, subgrains and high-density dislocation regions via hot rolling. The homogeneous deformation microstructure results in needle-like, high-density precipitates after artificial aging and decreases the stress concentration of load bearing, which is beneficial to the tensile properties and wear resistance of the composite. The wear behavior of the composites improves with Mg2Si-particle refinement and microstructural homogeneity. Keywords: Hot rolling, T6 treatment, Mechanical properties, Wear behavior, Al–Mg2Si in situ composite

The mechanical properties of Al-Si-Mg-Cu cast alloys are heavily determined by Cu content due to the precipitation of relating strengthening precipitates during the aging treatment. In this study, the microstructures and mechanical properties of Al-9Si-0.5Mg-xCu (x = 0, 0.9, 1.5, and 2.1 wt.%) alloys were investigated to elucidate the effect of Cu content on the evolution of their mechanical properties. After T6 (480 °C + 6 h − 530 °C + 4 h, 175 °C + 10 h) treatment, Mg-rich and Cu-rich phases were dissolved in the matrix; the main aging-precipitates of the alloys change from the needle-like β″ phases in the base alloy to the granular Q′ phases in the 0.9Cu alloy, the granular Q′ phase in the 1.5Cu alloy, the granular Q′ phase, and θ′ platelets in the 2.1Cu alloy. The increase of Cu level results in difference of the type, number density, and morphology of the nanoscale precipitated phase. Because of precipitation strength, the yield strength was increased by 103–130 MPa depending on the Cu contents. The precipitation strengthening effect of the precipitates was quantitatively evaluated by the Orowan mechanism. The aging-treated Al-9Si-0.5Mg-2Cu alloy shows the good strength and ductility: yield strength 351 MPa, ultimate tensile strength 442 MPa, and elongation 8.4%. The morphologies of fracture surfaces of the alloys also were observed.

The hot deformation behaviors of homogenized direct-chill (DC) casting 6061 aluminum alloys and Mn/Cr-containing aluminum alloys denoted as WQ1 were studied systematically by uniaxial compression tests at various deformation temperatures and strain rates. Hot deformation behavior of WQ1 alloy was remarkably changed compared to that of 6061 alloy with the presence of α-Al(MnCr)Si dispersoids. The hyperbolic-sine constitutive equation was employed to determine the materials constants and activation energies of both studied alloys. The evolution of the activation energies of two alloys was investigated on a revised Sellars’ constitutive equation. The processing maps and activation energy maps of both alloys were also constructed to reveal deformation stable domains and optimize deformation parameters, respectively. Under the influence of α dispersoids, WQ1 alloy presented a higher activation energy, around 40 kJ/mol greater than 6061 alloy’s at the same deformation conditions. Dynamic recrystallization (DRX) is main dynamic softening mechanism in safe processing domain of 6061 alloy, while dynamic recovery (DRV) was main dynamic softening mechanism in WQ1 alloy due to pinning effect of α-Al(MnCr)Si dispersoids. α dispersoids can not only resist DRX but also increase power required for deformation of WQ1 alloy. The microstructure analysis revealed that the flow instability was attributed to the void formation and intermetallic cracking during hot deformation of both alloys.

In order to improve the comprehensive properties of casting aluminum, and to fulfill the requirements of forming thin wall fins for communication products, mechanical stirring was employed to prepare the semi-solid aluminum alloy AlSi8. communication products were produced by the semi-solid die casting process. The microstructure and mechanical and thermal properties were studied. The test results show that the microstructure of semi-solid die-casting samples changes from dendrite to globular microstructure, and the average tensile strength, elongation and thermal conductivity are 220MPa, 7% and 170 W/(m*K), respectively, which is significantly higher than that of the common die-casting samples. It was proved that the semi-solid die casting technology can be used in actual production and improve the products quality.

Sedimentation of free-floating grains is the main origin of the negative centerline segregation in direct-chill casting of aluminum alloys. This study examines the motion and distribution of the floating grains during casting using experimental measurements and numerical modeling. The typical floating grains consisting of interior solute-lean coarse dendrites and periphery fine dendrites were experimentally observed only in the central region of the billet along with the negative segregation. The billet exhibits the strongest segregation at the center where the most floating grains are found. In simulations, under the action of the convection and the underlying forces, the grains floating in the transition region exhibit different motion behaviors, i.e., settling to the mushy zone, floating in the slurry zone, and moving upward to the liquid zone. However, most grains were transported to the central region of the billet and then were captured by the mushy zone and settled. Therefore, the floating grains comprise the largest share of the grain structure at the center of the billet, in agreement with the experimental results. Moreover, the simulation results indicate that the increased size of the grains promotes the sedimentation of the floating grains. These results are important for the future alleviation of negative centerline segregation in direct-chill casting of aluminum alloys.

The effects of casting speed on macrosegregation and grain structure during the direct-chill casting of an Al–Mg–Si alloy are experimentally investigated. Results show that increasing the casting speed yields a more pronounced negative centerline segregation. Regard this mechanism, apart from the increased contribution of solidification shrinkage, the variation in floating grains is newly observed. The increased casting speed significantly increases the size and fraction of floating grains at the central portion of the billet, thus resulting in a more severe negative segregation. To clarify the experimentally observed phenomena, the solidification and distribution of floating grains in billets cast at different casting speeds are numerically simulated. The increased casting speed deepens the slurry zone significantly, thus providing more time for the floating grains to freely float and develop before settling into the mushy zone. Additionally, the greater slope of the coherency isotherm resulting from the increased casting speed promotes the movement and sedimentation of the floating grains toward the central portion of the billet. Consequently, more floating grains are detected at the billet center. [ABSTRACT FROM AUTHOR]