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In this paper, the effect of deep cryogenic treatment (DCT) on the microstructure and properties of automotive 6063 aluminum alloy at different times was investigated with automotive 6063 aluminum alloy as the research object. The results show that under the conditions of deep cryogenic treatment, the lattice distortion occurs in the alloy matrix microstructure, and the resulting internal stress promotes the large proliferation of dislocations within the alloy and the increase of dislocation density; meanwhile, after the deep cryogenic treatment, the deformed grains are transformed into recrystallized and sub-crystals structural grains, the grains are refined, and the size of the grains is refined from the original 25.2 μm to 20.3 μm, with fine equiaxed crystals. Among them, the mechanical properties of the DCT36h specimen were the best, and its hardness, tensile strength, yield strength and elongation reached 142.44 HV, 328.32 MPa, 177.42 MPa, and 29.29%, which were 34.17%, 5.62%, 11.10%, and 32.77% higher than the original sample, respectively. We believe that the main mechanism for the increase in toughness is multiple reinforcement such as dislocation strengthening, grain refinement strengthening, precipitated phase strengthening and texture strengthening. [ABSTRACT FROM AUTHOR]

This study aimed at the preparation of a 2024 aluminum alloy (2024Al) matrix composite with high strength, high toughness and high magnetic properties that can be used in practical applications. Therefore, Nd2Fe14Bp/2024Al–Co composites with different Co contents (wt.%) were prepared by ball milling, cold isostatic pressing and microwave sintering. The effects of the Co content on the microstructure, mechanical properties and magnetic properties of the prepared composites were studied. Under the conditions of the sintering temperature of 490 °C, heating rate of 20 min/°C and soaking time of 30 min, it was found that with the increase in Co content (0→2.5%→5%→7.5%→10%), the grain size first decreased and then increased, and reached the optimal value of about 3–5 μm when the Co content was 7.5%, with the microstructure being relatively uniform. At the same time, the compactness of the composite arrived at a maximum of 95.4%. The main particle phases in the composite were Nd2Fe14B, Nd2 (Fe, Co)14B and Co particles. In the nanoindentation test, the interface strength of the 7.5% Co sample was significantly higher than that of the Co-free sample. In addition, the microhardness, yield strength and compressive strength of the 7.5% Co sample were 152 HV, 210 MPa and 269 MPa, respectively, which increased by 67%, 78% and 75%, respectively, compared with the Co-free sample. With the increase in Co content, the remanence (Br), coercivity (Hcj) and maximum magnetic energy product ((BH) max) of the composites first increased and then decreased. When the Co content was 7.5%, the three performance indicators reached their optimum values, which were Br: 0.20 (T), Hcj: 4.6 (kOe) and (BH)max: 28.36 (kJ/m3). The expected goal of the lightweight magnetic materials was achieved, and the action mechanism of Co addition in the composites was also analyzed in detail. [ABSTRACT FROM AUTHOR]

Abstract In this study, the nanometer in-situ γ-Al 2 O 3 particles reinforced aluminum matrix composites was successfully fabricated by the A356 aluminum alloy and Co 3 O 4 powder at 850 °C by means of in-situ reaction in the high temperature melt. The effects of γ-Al 2 O 3 particle and cobalt element on the microstructure and properties of the composites were investigated in detail. The endogenous γ-Al 2 O 3 and cobalt could modify the coarse plate like eutectic Si into fine fibrous like and refine the second dendrite arm spacing (SDAS) of the grains simultaneously. When the content of cobalt was lower than 0.57% and content of γ-Al 2 O 3 particles was lower than 0.6 vol%, the particles distributed uniformly in the grain, however, when the particulate amount was up to 0.8 vol%, the particles would distribute at the grains boundaries or form as a rodlike phase. The grain size was sharply refined to 200 μm when the particulate content was 0.8 vol%. It was found that the ultimate tensile strength (UTS), elongation of the 0.6 vol% γ-Al 2 O 3 /A356 composites had arrived at the maximum that had enhanced by 43.6% and 85.7% in comparison to the matrix respectively, which were attributed to the homogeneous distribution of the nanoparticles, the refinement of the SDAS of the α-Al grains and the modification of the eutectic Si phases. Highlights • Co 3 O 4 power can react with Al to produce nanometer γ-Al 2 O 3 particles in A356 melt. • The produced Al 2 O 3 and cobalt can modify Si phase and refine α-Al dendrite. • The best addition amount of γ-Al 2 O 3 is 0.6 vol% and cobalt is 0.57%. • The UTS increases by 43.6% and the El increases by 85.7% compared with A356 matrix. [ABSTRACT FROM AUTHOR]

• Al and Co 3 O 4 were employed to fabricated nano Al 2 O 3 reinforce Al matrix composite. • High density dislocation has been found around the nano γ-Al 2 O 3 particles. • The submicron Al 9 Co 2 particles can restrict the grain boundary moving. • The best addition amount of γ-Al 2 O 3 is 0.6 vol%. The nanometer and uniform distributed in-situ γ-Al 2 O 3 particles reinforced aluminum matrix composites have been successfully fabricated in the Al-Co 3 O 4 components at 850 °C by means of direct melt reaction method. The microstructure and properties of composites were investigated. The nanometer γ-Al 2 O 3 distributes uniformly in the matrix and is assumed as γ-Al 2 O 3 that is a stable phase of Al 2 O 3 when the temperature is lower than 1000 °C. The Al/γ-Al 2 O 3 interface is clean with certain matching degree. High density dislocation has been found around the nano γ-Al 2 O 3 particles. At the grain boundary the submicron Al 9 Co 2 particles exist, which can restrict the grain boundary moving. The tensile properties of 0.6 vol% γ-Al 2 O 3 sample arrives at utmost while the 0.8 vol% sample decrease a lot due to the particle agglomeration. [ABSTRACT FROM AUTHOR]

Abstract: The as-cast in situ Al2O3 particles reinforced aluminum matrix composites were subjected to the impact treatment due to the Lorentz force generated by high pulsed electromagnetic field. The magnetic induced intensity (B) was set as 1T, 2T and 3T. Transmission electronic microscopy observation shows that the impact has induced the elastic deformation in materials that results in the enhancement of dislocation density. The value increases from 2.2×1011/m2 in as-cast sample to 8.9×1013/m2 in the 3T treated one. Besides, stacking faults and deformation twins with 3, 4, 6 atomic planes can also be seen. The results demonstrate that high pulsed electromagnetic field is an efficient and economical approach to acquire a specific microstructure and, meanwhile, keep the original shape of sample. [Copyright &y& Elsevier]

Abstract: The aluminum matrix composites reinforced by Al2O3 and Al3Zr particulates were fabricated via in situ chemical reaction between Al–15wt.% Zr(CO3)2 systems. In the process of in situ reaction, a low frequency electromagnetic field (EMF) is employed to improve the conditions of reaction between reactants powder and melt. The optimized electromagnetic density of low frequency EMF is 0.025T. During the direct chill casting process of composites melt, the custom-designed electromagnetic fields are introduced to control the microstructures and improve the billet surface quality. XRD analysis shows that Al2O3 and Al3Zr reinforcement phases have been obtained. The Lorenz force improves the kinetic condition and accelerates the nucleation of endogenetic particulates. Microstructure analysis by SEM indicates that the average size of particulates and grain size of matrix are refined to 0.5–1μm and 20–40μm, respectively. The surface quality of round billet is greatly improved by the high frequency EMF. The results of tensile properties test show that the tensile strength of composites in situ fabricated with EMF is 254.6MPa, which is increased by about 104MPa and 69.4% compared with those of composites in situ fabricated without EMF. [Copyright &y& Elsevier]

Abstract: Al2O3p/Al composites were prepared by direct melt reaction process. The thermodynamics of in situ chemical reactions between molten aluminum and CeO2 powder was studied. The XRD results show that the components of the as-prepared composites consist of Al2O3 and Al phases. For the as-cast composite specimens, SEM, EDX, TEM and SAD were used to analyze the reinforcement phases and interface characters of composites. The results show that the in situ generated Al2O3 particles, whose sizes are 100–200nm, have various irregular shapes and disperse uniformly in matrix. TEM observation shows that the interface between particle and matrix is clean. Furthermore, there is no fixed orientation relationship between Al2O3 particles and aluminum matrix. Only orientation parallel relationship with low exponent is found. Therefore, the composites have isotropic properties. Besides characters mentioned above, there are large amount of high density dislocations and the generated extensive fine subgrains around Al2O3 particles. These features are favorable for improving composite performances. As a result, the composites are comprehensively strengthened not only by Al2O3 particles, but also by the high density dislocations and fine subgrains. [Copyright &y& Elsevier]

• HEA particle clusters decrease and particles distribute more homogeneously with increasing rolling reduction. • Hot rolling improves the micro-nanomechanical properties of 2024Al matrix, interface and HEA reinforcement. • Hot rolling is conducive to improving the interface bonding between HEA particles and 2024Al matrix. • The dynamic recrystallization type is continuous dynamic recrystallization. [Display omitted] The FeCoNi 1.5 CrCu/2024Al composites fabricated by microwave sintering were hot rolled to investigate the effect of hot rolling reduction on microstructure, mechanical properties and macroscopic crystal structure. The results show that when the rolling reduction is 62.5%, the refining effect of reinforced particle clusters is obvious, and the large-size reinforced particle clusters have basically disappeared. Besides, it distributes homogeneously in the matrix along the rolling direction, and the grain size of matrix is significantly reduced. With the increase of reduction, the relative density and microhardness of the composites increase first and then decrease, reaching the maximum of 96.6% and 172.5HV at 62.5%, respectively. Hot rolling is conducive to improving the interface bonding between HEA particles and 2024Al matrix. And when rolled with 62.5% reduction, the micro-nanohardness and elastic modulus at the interface reach 1715 MPa and 83.93 GPa, respectively. The tensile strength of hot-rolled composites increases rapidly first and then slowly, and the elongation decreases rapidly first and then slowly. When at the optimum rolling reduction 62.5%, the tensile strength and elongation of composites reach 173.54 MPa and 12.93%, respectively. The strengthening mechanisms are mainly grain refinement strengthening, load transfer strengthening and Orowan strengthening. [ABSTRACT FROM AUTHOR]

In this study, A356 matrix and 0.2 vol.%∼0.8 vol.% in-situ Al 2 O 3p /A356 composite were hot rolled to 75% reduction ratio and 0.6 vol.% composite was hot rolled to 75% and 83% reduction ratios. Scanning electron microscope (SEM), electron back scattering diffraction (EBSD) and transmission electron microscopy (TEM) were used to characterize the microstructure and texture evolution so as to investigate the effect of the particle content and reduction ratios. In the 75% rolling reduction, the Si phase in the A356 matrix and Al 2 O 3p /A356 composites was fragmented and distributed along the rolling direction (RD), obvious Al 2 O 3 agglomeration diminished. On the state of 75% reduction, when the content of Al 2 O 3 was 0.2 vol.%, the composite had the finest grain size, however the 0.6 vol.% composite had a better Si phase and Al 2 O 3 distribution. The Al 2 O 3 particle in 0.2 vol.% sample can enhance the dislocation density and accelerate the sub-grain boundary formation. For the 75% reduction materials, the tensile properties increased with the increase of particulate content to 0.6 vol.% then decreased. The mechanical properties of 83% rolling reduction sample was better than the 75% reduction. Tensile tests showed that the ultimate tensile strength (UTS), yield strength (YS) and elongation (El) of 0.6 vol.% Al 2 O 3p /A356 composite increased to 282 MPa, 221 MPa and 17.5%, respectively, due to the uniform distribution of the particles and refined Si phase upon increasing the rolling reduction to 83%, in combination with T4 heat treatment. In addition, the mechanisms of particle dispersion, recrystallization grain refinement and strengthening are also discussed. Image 1 • Hot-rolling can break the Si phase into small particles and make the Al 2 O 3 particles uniformly distributed. • The 0.6 vol% composite has the best mechanical properties. • Compared with the as-cast state 0.6 vol% composite, the UTS of the 83% reduction 0.6 vol% composite after T4 heat treatment is nearly the same, the value is 282 MPa, in addition the El enhanced by 169%–17.5%. [ABSTRACT FROM AUTHOR]

In this investigation, FeCoNi 1.5 CrCu high-entropy alloy (HEA) was prepared by mechanical alloying, following which HEA particles reinforced 2024 aluminum matrix composites were obtained using a microwave with low-temperature sintering. The microstructural characterization and mechanical properties of the composites under different sintering time at isothermal temperature were investigated systematically. The results showed that HEA particles at first diffuse uniformly and then agglomerate with an increase in the sintering time. An interdiffusion (ID) layer exists between the HEA particle and the matrix, and high-density dislocations surround the interface of the HEA/2024Al composite, with a width of 80–120 nm. The hardness and elastic modulus of the interface was tested using nanoindentation technique, which presents excellent interface micro-domains with the mechanical strength reaching about 1331.1 MPa and 47.544 GPa. At 40 min of sintering time, the compressive strength, yield strength and microhardness of the composites were reaching the maximum of 248.7 MPa, 227.4 MPa and 93.1 HV, respectively. [ABSTRACT FROM AUTHOR]

In this study, the addition of Zr element (K 2 ZrF 6) was employed to improve the wettability, inhibit the serious chemical reaction of B 4 C to Al, and uniformly disperse the B 4 C particles in the Al melt, during the fabrication of B 4 C/Al composites via melt stirring method. And the particle distribution, interface microstructure and mechanical properties of the fabricated composites were further investigated. The metallography observation shows that the B 4 C particles could be effectively introduced to the Al melt with the addition of Zr element, while there were few B 4 C particles observed in the composites without Zr addition. The XRD analysis indicates that the ZrB 2 and ZrC peaks arise with the addition of Zr, where the ZrB 2 and ZrC have better chemical stabilization and wettability than the B 4 C ceramic particles. The SEM, EDS, TEM and SAED analysis shows that the ZrB 2 and ZrC interface layer with a thickness of about 200–350 nm on the B 4 C surface was formed, which could avoid the serious chemical reaction and improve the wettability of B 4 C to Al, simultaneously. In addition, the easy introduction of B 4 C particles to the Al melt with K 2 ZrF 6 , the formation mechanism of ZrB 2 and ZrC layer, and mechanical properties of the composites were also discussed. [ABSTRACT FROM AUTHOR]