Interfacial Microstructure And Thermodynamic Analysis Of AZ91D/6061 Bimetal Composite Interface

At present,bimetal composites are developing rapidly,among which magnesium/aluminum composites are widely used in automobile,aerospace and other fields.AZ91D/6061 composite ingots were prepared by solid/liquid composite casting process.The influence of the "liquid ratio" of semi-solid structure on the morphology of the composite interface was studied.The results show that AZ91 D magnesium alloy forms Al₁₂Mg₁₇ phase during solidification,and 6061 aluminum alloy precipitats Mg₂ Si and other second phases.According to Midema mathematical model,the standard enthalpy of formation of Al₃Mg₂ and Al₁₂Mg₁₇ phases are-0.40137 k J/mol and-0.4321 k J/mol,respectively.Thus,Al₁₂Mg₁₇ taks precedence over Al₃Mg₂ in solidification process.By Dictra dynamic modules of composite interface calculation and calculation model analysis,the diffusion rate of Mg atoms is greater than that of Al atoms.Mg atoms in the "liquid" of AZ91 D alloy semi-solid billet spread to the composite interface quickly,and combine with Al atoms in liquid alloy 6061 to form a priority single-phase organization: Al₁₂Mg₁₇.In addition,the relation between the diffusion coefficient,concentration and migration distance of Al and Mg atoms is calculated as:The microstructure of AZ91D/6061 bimetallic composite interface is composed of Al-Mg matrix,Al₃Mg₂ and Al₁₂Mg₁₇ phases.Combined with composite interface,thermodynamics and kinetics calculation results reveal that the solid/liquid composite casting AZ91D/6061 metallurgical bonding mechanism of bimetal composite interface is: liquid metal fusion and coagulation combined with solid metal is main,semi-solid metal alloy blank "liquid" area atomic diffusion migration priority separation in the second phase is complementary with solidification.Figure 46;Table 4;Reference 81...