Process Research On Al-7%Si/Al-22%Si Alloy Bimetal Composite By Semi-solid Thixo-forging

In this work, the process parameters and technical characteristics of Al-7wt.%Si alloy and Al-22wt.%Si alloy bimetal composite parts by semisolid metal process were investigated by numerical simulation and semi-solid thixo-forging, and the interface microstructure and properties of bimetal composite parts were analyzed.The constitutive relation equations of Al-7wt.%Si alloy and Al-22wt.%Si alloy were established based on the existing rheological mechanics model of the corresponding semi-solid metal. The effect of the operating temperatures of the semi-solid billets, the mould temperatures and the forging speed on the formation of Al-7wt.%Si alloy/Al-22wt.%Si alloy bimetal composite were analyzed by Deform-3D finite element analysis software, and the optimized parameters were obtained:operating temperature for Al-7wt.%Si semisolid billets and Al-22wt.%Si semisolid billets were580℃and575℃, respectively; temperature for the upper mold and lower mold were100℃and200℃, respectively; punch velocity was20mm/s; and the squeezing holding time was3seconds.OM, SEM, Micro-hardness Test, and Tensile Test were utilized to analyze the macro/micro-structure and properties of the bimetal composite samples prepared under the optimal process parameters. The observation of the macrostructure indicated that the edge of the composite interface bended to wrap up and the bimetal composite was of good shape, a complete filling was achieved; no macro pores, impurities, oxide and cracks were found at the interface. The microstructure and component analysis indicated that the two typical semi-solid matrixes mutually diffused at the interface and formed a good metallurgical bonding. The results of the mechanical property test showed that there was a smooth and gentle gradient change for the hardness at the interface transition; and the average hardness at the interface reached90HV. Tensile strength and shear strength of the bimetal composite at the interface was157MPa and118MPa, respectively. This indicates a good metallurgical bonding was obtained.