Study On The Interface Of Magnesium Alloy/Stainless Steel Via Liquid-solid Compound Casting Process

Magnesium alloy is the lightest metal structural material in industrial applications,because of a serious of advantages,such as high specific strength and specific stiffness,abundant resources,easy to recycle.Steel is the most widely used structure material in modern industry,owing to its consistent properties,excellent ductility and lower material and fabrication costs.If the effective combination of magnesium alloy/stainless steel bimetal materials can be achieved,it will be advantageous in achieving light weight and have a broad application prospect.However,the physical,chemical and mechanical properties between Mg and Fe have a great difference,and Mg and Fe do not dissolve or react with each other.In order to achieve effective connection between magnesium alloy and stainless steel,firstly,the stainless steel are treated with surface preparation,then,a liquid-solid compound casting process,which is a new method to prepare bimetal materials,is used to obtain magnesium alloy and stainless steel bimetal composite casting.Following conclusions can be conclude according to the study and analyze of the compound interface:（1）The stainless steel cross-section which is mechanically polished is notch.The surface appearance of stainless steel is furrow,and the surface has a certain degree of roughness,and there is no contaminant such as rust on the surface.（2）After surface treatment by hot-dipping aluminum,the cross-section has two sub-layers:the outer layer is an Al-rich layer and the middle layer is a Fe-Al layer.The thickness of the coating increases with the increasing of hot-dipping time,and needle-like FeAl₃ phase precipitates in the Al-rich layer.The surface of Al coating has a rough sheet structure and a dense layer of Al₂O₃ oxide film is formed on the surface.（3）Mechanically bond is obtained between magnesium alloy and stainless steel bimetal materials obtained by the mechanical grinding surface treatment method,and there is a clear gap at the interface,also no intermediate layer is formed,and no new phase is generated.（4）Metallurgical bond is achieved between magnesium alloy and stainless steel bimetal materials by the hot-dipping aluminum surface treatment method,and the interface is divided into two reaction layers.The reaction layer I near the magnesium matrix is mainly composed ofα-Mg,Al₁₂Mg₁₇,FeAl₃ and MgAl₂O₄;reaction layer II close to stainless steel consists of a single Fe₂Al₅ phase.The thickness of interface reaction zone increases with the increasing of time of hot-dipping aluminum.（5）The microhardness of layer is higher than that of magnesium matrix,and the microhardness of layer II is the highest.The average microhardness of layer I is 158 HV,and the average microhardness of layer II is 493HV.Although layer I also has a Fe-Al phase,but the content of Fe-Al phase is small,and the amount ofα-Mg solid solution is relatively high.Therefore,the microhardness of layer I is smaller than that of layer II.（6）The shear strength of the magnesium alloy/stainless steel interface obtained by the hot dipping aluminum surface treatment method is significantly higher than that of the magnesium alloy/stainless steel bond interface obtained by the mechanical grinding surface method.The shear strength of the magnesium alloy/stainless steel interface obtained by the hot dipping aluminum at 780℃and 75s,which is highest,is 26.8MPa.And with the increasing of hot dip time,the thickness of interface reaction layer increases,however,the shear strength of the compound interface decreases.