Study On Interface Of Al/Mg Bimetal Produced By Lost Foam Casting Liquid-liquid Compound

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.In this paper,Al/Mg bemetallic castings were prepared by liquid-liquid process of lost foam casting.The metallurgical composite of aluminum alloy and magnesium alloy was successfully achieved without mixing of liquid metal by setting the metal interlayer.The influences of the interlayer material,interlayer thickness and pouring temperature on the effect of Al/Mg bemetallic castings prepared by LFC were investigated.The interface characteristics and mechanical property characteristics of Al/Mg bemetallic castings such as macroscopic morphology,micromorphology,interfacial phase composition and element distribution,defect,hardness and bond strength were analyzed,and the interface formation mechanism of Al/Mg bemetallic is discussed.The Al/Mg bimetallic composites were successfully fabricated by the LFC liquid-liquid compound process with a Al interlayer.A compact metallurgical interface was formed between the AZ91D substrate and the A356 substrate.The metallurgical interface of the Al/Mg bimetallic composites included two reaction layers.The reaction layer near the AZ91D substrate consists of Al₁₂Mg₁₇ and?-Mg.The reaction layer near the A356 substrate was composed of Mg₂Si and Al₃Mg₂ phases.The effect of the thickness of Al interlayer and pouring temperature on the Al/Mg bemetallic castings prepared by liquid-liquid LFC process was investigated.When the thickness of the Al interlayer is 2 mm,the Al interlayer can successfully prevent the mixture of two kinds of liquid alloys,and can form a sound metallurgical bond with those two kinds of liquid alloys.When the pouring temperature is 730°C,the quality of Al/Mg bimetallic castings is the best,and the microstructure of each reaction layer is fine and uniform without any defects.The Al/Mg bimetallic composites were successfully fabricated by the LFC liquid-liquid compound process with a Zn interlayer.There are two reaction layers formed between the AZ91D substrate and the A356 substrate.The reaction layer near the AZ91D substrate was Al₅Mg₁₁Zn₄,?-Mg and MgZn.The reaction layer near the A356 substrate was composed of Mg₂Si,Mg₃₂?Al,Zn?₄₉ and?-Al phases.The effect of the thickness of Al interlayer and pouring temperature on the Al/Mg bemetallic castings prepared by liquid-liquid LFC process was investigated.The test results with 3 mm Zn interlayer are the best,and a wider reaction layer was formed between the AZ91D and the A356 with less amount of hole.When the pouring temperature is 700°C,the bonding quality of the Al/Mg bemetallic castings is better,and the Zn interlayer has formed distinct interfaces with the Mg substrate and Al substrate respectively.The mechanical properties of Al/Mg bimetallic composites with Al interlayer or Zn interlayer were tested.Whatever the interlayer is,the hardness of the reaction layer is obviously higher than that of the substrate.When the Al interlayer is used,the hardness value of the reaction layer near the AZ91D is 167-210 HV.The hardness value of the reaction layer near the A356 is 250-299 HV.When the Zn interlayer is used,the hardness value of the reaction layer near the AZ91D is 175-195 HV,and the hardness value of the reaction layer near the A356 is 223-325 HV.When the Al interlayer is used,the corresponding shear strength of the pour temperature at 710°C,730°C and 750°C is 1.86MPa,9.14 MPa and 6.11 MPa,respectively.When the Zn interlayer is used,the shear strength of Al/Mg bimetallic composites is 10.91 MPa.The interface formation mechanism of Al/Mg bimetallic composites prepared by liquid-liquid LFC process with interlayer was analyzed.Whether Al or Zn interlayer is used,the formation process of the interface can be divided into four stages:filling,melting and diffusion,metallurgical reaction and solidification.The interlayer is completely melted after successfully preventing liquid alloy mixed together and has metallurgical reaction with liquid alloy,then the metallurgical Al/Mg bimetallic composites is obtained.