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• Microstructure and mechanical behavior of Al-xSi/AZ91D bimetallic composites were studied. • Thickness of interface of Al/Mg bimetallic composites decreased with increasing Si content. • Oxide inclusion defects in interface layer decreased with increasing Si content. • Increasing Si content resulted in an inconsistent preferred orientation of interface layer. • Shear strength of the composites increased with increasing Si content, obtaining a maximum value with 15 wt.% Si. In this paper, the effect of the Si content on microstructure evolution, mechanical properties, and fracture behavior of the Al-xSi/AZ91D bimetallic composites prepared by compound casting was investigated systematically. The obtained results showed that all the Al-xSi/AZ91D bimetallic composites had a metallurgical reaction layer (MRL), whose thickness increased with increasing Si content for the hypoeutectic Al-Si/AZ91D composites, while the hypereutectic Al-Si/AZ91D composites were opposite. The MRL included eutectic layer (E layer), intermetallic compound layer (IMC layer) and transition region layer (T layer). In the IMC layer, the hypereutectic Al-Si/AZ91D composites contained some Si solid solution and flocculent Mg 2 Si+Al-Mg IMCs phases not presented in the hypoeutectic Al-Si/AZ91D composites. Besides, increasing Si content, the thickness proportion of the T layer increased, forming an inconsistent preferred orientation of the MRL. The shear strengths of the Al-xSi/AZ91D bimetallic composites enhanced with increasing Si content, and the Al-15Si/AZ91D composite obtained a maximum shear strength of 58.6 MPa, which was 73.4% higher than the Al-6Si/AZ91D composite. The fractures of the Al-xSi/AZ91D bimetallic composites transformed from the T layer into the E layer with the increase of the Si content. The improvement of the shear strength of the Al-xSi/AZ91D bimetallic composites was attributed to the synergistic action of the Mg 2 Si particle reinforcement, the reduction of oxidizing inclusions and the ratio of Al-Mg IMCs as well as the orientation change of the MRL. [ABSTRACT FROM AUTHOR]

In this paper, a Ni coating was deposited on the surface of the A356 aluminum alloy by high velocity oxygen fuel spraying to improve the performance of the AZ91D magnesium/A356 aluminum bimetal prepared by a compound casting. The effects of the Ni coating as well as its thickness on microstructure and mechanical properties of the AZ91D/A356 bimetal were systematically researched for the first time. Results demonstrated that the Ni coating and its thickness had a significant effect on the interfacial phase compositions and mechanical properties of the AZ91D/A356 bimetal. The 10µm's Ni coating cannot prevent the generation of the Al-Mg intermetallic compounds (IMCs) at the interface zone of the AZ91D/A356 bimetal, while the Ni coating with the thickness of 45 µm and 190 µm can avoid the formation of the Al-Mg IMCs. When the Ni coating was 45 µm, the Ni coating disappeared and transformed into Mg-Mg 2 Ni eutectic structures+Ni 2 Mg 3 Al particles at the interface zone. With a thickness of 190µm's Ni coating, part of the Ni coating remained and the interface layer was composed of the Mg-Mg 2 Ni eutectic structures+ Ni 2 Mg 3 Al particles, Mg 2 Ni layer, Ni solid solution (SS) layer, Al 3 Ni 2 layer, Al 3 Ni layer and sporadic Al 3 Ni+Al-Al 3 Ni eutectic structures from AZ91D side to A356 side in sequence. The interface layer consisting of the Mg-Ni and Al-Ni IMCs obtained with the Ni coating had an obvious lower hardness than the Al-Mg IMCs. The shear strength of the AZ91D/A356 bimetal with a Ni coating of 45 µm thickness enhanced 41.4% in comparison with that of the bimetal without Ni coating, and the fracture of the bimetal with 45µm's Ni coating occurred between the Mg matrix and the interface layer with a mixture of brittle fracture and ductile fracture. [ABSTRACT FROM AUTHOR]

In this work, SiC np /Al6082 aluminum matrix composites were prepared by squeeze casting (SC) combined with stir casting, and the effects of nano-sized SiC particles (SiC np) and SC on microstructure and mechanical properties of the 6082 aluminum alloy were investigated. The result shows that the SiC np were uniformly distributed in the 6082 aluminum matrix alloy using the stir casting. With the addition of the SiC np , the microstructure of the 6082 aluminum alloy was obviously refined, up to 30.55% grain refinement compared to the 6082 aluminum alloy without the addition of the SiC np. The as-cast ultimate tensile strength, yield strength and elongation of the SiC np /Al6082 aluminum matrix composites were enhanced, which increased by 8.92%, 12.16%, and 12.60%, respectively, compared with the 6082 matrix alloy without the SiC np. After the SC, the compactness of the SiC np /Al6082 composites was significantly improved, and the grain of the composites was further refined. The ultimate tensile strength, yield strength and elongation of the SiC np /Al6082 composites fabricated by the SC respectively increased by 29.81%, 43.18%, and 226.28%, compared to the 6082 aluminum alloy obtained by gravity casting (GC). [ABSTRACT FROM AUTHOR]

In the present work, a novel Ni-Cu composite interlayer was prepared on the surface of A356 aluminum alloy solid insert using the chemical nickel-plating and electro-coppering technology, in order to restrain the generation of brittle phases and enhance the shear strength of A356 aluminum/AZ91D magnesium bimetal manufactured using a compound casting. The effect of the Ni-Cu composite interlayer on the microstructure, mechanical properties and corrosion resistance of the bimetal was studied. The results show that the Ni-Cu composite interlayer effectively restrained the generation of the brittle and hard Al-Mg intermetallic compounds (IMCs). The interface layer of the A356/AZ91D bimetal without Ni-Cu composite interlayer was composed of Al 3 Mg 2 , Al 12 Mg 17 , δ-Mg and Mg 2 Si phases, while the interfacial reactants of the A356/AZ91D bimetal with Ni-Cu composite interlayer were mainly Al 3 Ni, Ni (Cu), Cu (Ni), Mg 2 Cu and Al 7 Cu 3 Mg 6 phases. With the application of the Ni-Cu composite interlayer, the thickness of the interface of the A356/AZ91D bimetal remarkably decreased from 1400 μm of the sample without Ni-Cu composite interlayer to 40 μm. The shear strength of the A356/AZ91D bimetal using Ni-Cu composite interlayer increased by 20.3 % compared with that of the bimetal without Ni-Cu composite interlayer. The fractures of the A356/AZ91D bimetals with and without Ni-Cu composite interlayers belonged to a brittle rupture mode. The breakage of the bimetal with Ni-Cu composite interlayer mainly took place between the Ni-Cu layer and AZ91D matrix, while the rupture of the A356/AZ91D bimetal without Ni-Cu composite interlayer was located in the interface layer. The Cu(Ni) and Ni(Cu) layers had a lower nano-hardness than the Al-Mg IMCs, and the elasticity modulus for the Cu(Ni), Ni(Cu) and Al 3 Ni phases were higher compared to those of the Al-Mg IMCs. The results of corrosion test exhibited that the Ni-Cu composite interlayer had little influence on the corrosion resistance of the A356/AZ91D bimetal. [ABSTRACT FROM AUTHOR]