Study On Interfacial Microstructure And Mechanical Properties Of A356/6082 Bimetal Fabricated By Solid-liquid Rolling

The layer-metal composite combines the advantages of two or more components to overcome the defects and deficiencies of a single metal or alloy during service.At present,it has been widely used in aerospace,the petrochemical industry,machinery manufacturing,automotive electronics,daily supplies and other fields.In this paper,the microstructure and properties of A356/6082 laminated bimetal by solid-liquid rolling were investigated by means of optical microscope,scanning electron microscope and mechanical property test.By adjusting the pouring temperature of the cladding A356 aluminum alloy,the thickness of bimetal and the subsequent heat treatment parameters,the relationship between the microstructure evolution,elemental diffusion and mechanical properties of the interface betwee n A356 aluminum alloy and 6082 aluminum alloy during the composite process was emphatically illustrated.The elemental diffusion mechanism and fracture failure characteristics at the interfacial region are discussed.The results are as follows:(1)When the pouring temperature is too high,fine eutectic silicon accumulates at the interface owing to the strong chilling effect in the interfac ial region,hindering the further diffusion of alloy elements.In addition,coarse microstructure and severely segregated eutectic silicon are formed on the side of A356 aluminum alloy.When the pouring temperature is low,the oxide film on the substrate surface is broken and the wettability of the two alloys is improved,but the alloy melts contains less energy so that the transition region between the A356 aluminum alloy and 6082 aluminum alloy only form a mechanical bond under rolling force.When the pouring temperature is 660 ?,?-Al phase and eutectic silicon in the interface zone of bimetal are evenly distributed.The interface region of bimetal achieves the good metallurgical bond,where the element diffusion width is about 93 ?m and the shear strength of A356/6082 bimetal can reach up to 114.2 MPa.With the decrease of pouring temperature,the ultimate tensile strength of bimetal gradually is improved.The pouring temperature is 620 ?,the ultimate tensile strength reaches up to 205 MPa,and the fracture location occurs firstly in the side of A356 aluminum alloy.Nevertheless,the micro-hardness value of transition region suddenly changes from 82.4 HV to 61.5 HV.(2)When the rolling thickness is relatively thin,eutectic Si deposition phenomenon appears at the interface,stacking width is about 48 ?m.The Si-rich region of the A356 aluminum alloy is adjacent to the interface side,and a small amount of Si particles are precipitated.When the rolling thickness is large,the remelting thickness of substrate surface may be too large or even melt through.When the rolling thickness is 4.0 mm,the wettability between the cladding metal and the substrate is improved.The microstructure of the interface area is uniform,and the elements such as Al,Mg and Si in the alloys on both sides are fully diffused.The shear strength of bimetal can reach up to 118.4 MPa.And with the increase of rolling thickness,its shear strength gradually decreased,while the tensile strength gradually increased.When the rolling thickness is 2.5 mm,tensile strength is about 245.3 MPa.(3)The necking,melting and spheroidization of eutectic sil icon on the side of A356 aluminum alloy occurs with the increase of the heat treatment temperature.Moreover,spheroidization first occurs at the interface of bimetal.The shear strength value of the interfacial zone is gradually increased.With the prolongation of the holding time,the effect on the low temperature is not significant,and the alloy grains can be coarsened at high temperature.When the heat treatment temperature is 550 ?and the holding time is 1h,microstructure of the bimetal interface is uniform and the silicon particles are fine and round.Furthermore,there is no harmful reaction in the interfacial region.We can see that the elements in the interfacial region are fully diffused and the diffusion width is about 136 ?m,and the maximum shear strength of bimetal is about 145 MPa.In addition,when the composite interface is subjected to uniform shearing,the fracture form of the bimetal is brittle fracture.At the same heat treatment temperature,the diffusion velocity of Si atom is the max imum and that of Al atom is the minimum.The effect of holding time on the bimetal is smaller than the temperature parameter.