Investigation Of Microstructures And Mechanical Properties Of Al/Mg Bimetal Produced By Lost Foam Casting

Currently,magnesium and aluminum alloys are widely applied in vehicle construction and aerospace industries because of their excellent characteristic.However,sometimes,one of these alloys alone is difficult to meet the demands of the integrated performance.The lost foam casting was a promising solution to achieve the joint the magnesium alloy and the aluminum alloy in order to improve the energy efficiency.The lost foam casting is a near net shape technology for producing complex castings,which has great theoretical and practical significance in preparing the Al/Mg bimetal.In this paper the influences of pouring temperature,vacuum degree,melt-to-solid volume ratio?VR?and cross section position on the microstructures and properties of Al/Mg bimetallic castings prepared by LFC were investigated.The main studies and results are as following:?1?The Al/Mg bimetallic composites have been prepared successfully by lost foam casting.It can be found that the interface layers of the Al/Mg bimetallic composites with different pouring temperatures primarily consisted of three reaction layers:Al₁₂Mg₁₇+?-Mg eutectic,Al₁₂Mg₁₇+Mg₂Si and Al₃Mg₂+Mg₂Si.The formation mechanism of the interface of the Al/Mg bimetallic composites obtained by the LFC process can be explained by the fusion bonding and diffusion bonding.?2?The effect of the pouring temperature and vacuum degree on the microstructure and property of the Al/Mg bimetallic castings prepared by LFC was investigated.With increasing pouring temperature,the thickness of the interface layer increased significantly.The pouring temperatures have significant to the formation of defects.The pore defects with a large size are apparently present at the interface layer of the Al/Mg bimetallic composite with a pouring temperature of 710°C,while increasing pouring temperature to750°C,the thickness of the interface layer clearly exhibits an inhomogeneous morphology.A suitable vacuum degree also should be given in the process of compound casting.It is found that a big gap existed in the the interface of Al/Mg bimetallic casting with the vacuum degrees of 0MPa and 0.05MPa.In the vacuum degree of 0.01MPa there were the pore defects in the interface layer.Only with a pouring temperature of 730°C and a vacuum degree of 0.03MPa,a compact and uniform interface layer can be obtained.?3?The influence of the melt-to-solid volume ratio on the microstructure and property of the Al/Mg bimetallic castings prepared by LFC was also studied.With the increase of VR,the average thickness of the interface layer added.When the VR is 6.96,the interface is non-uniform,and some gaps are clearly detected;While further increasing VR to 42.33,the interface shows a non-uniform morphology,and some pore defects are observed;Only with a VR of 14.6 a compact and uniform reaction interface between aluminum and magnesium was obtained.?4?Based on previous research,the microstructure and property of different sections of the Al/Mg bimetal was analyzed.The interface layers of different sections of Al/Mg bimetallic casting also showed different morphologies.The thickness of the interface layer increased from top section to the bottom section apparently.There is a gap with a large size in the bottom section while the interface is not generated in the part of the position of the interface in the top section.Only in the middle section a compact and uniform interface layer can be get.?5?The Al/Mg bimetallic castings prepared by LFC were carried out mechanics performance testing.The result of microhardness test that the interface layers of the Al/Mg bimetallic composites had higher microhardnesses compared to the base metals,especially the Al3Mg2 phase,which indicated that the rigid and brittle phases have generated at the interface of the Al/Mg bimetallic composites.The push-out test demonstrated that the middle section of Al/Mg bimetallic composite with a pouring temperature of 730?,a vacuum of 0.03MPa,a VR of 14.6 obtained a maximum shear strength up to 47.67 MPa,showing an optimized bonding between the aluminum and the magnesium.The SEM fractograph of the push-out sample mainly showed a typical brittle fracture morphology due to the cracking of the Al₃Mg₂ and Al₁₂Mg₁₇ intermetallic phases.