Microstructure and Mechanical Properties of Extruded Al-Mg-RE Alloys

Microstructure and Mechanical Properties of Extruded Al-Mg-RE Alloys
　　Aluminum alloys have such characteristics as low density, high specific strength and rigidity, and have found a wide application in aeronautical and automotive industries. To extend the application field of aluminum alloys, some measures, which can improve the microstructure, strength and plasticity of aluminum alloys, have to be taken. Usually, the rare earth elements are recognized as one of the most effective elements available to improve both microstructure and property of aluminum alloys. And thus, research concerning the action of rare earth elements in aluminum alloys is of both important theoretical referring value and practical directing significance for developing neodymium magnets new aluminum alloys with high strength and ductility.In this investigation, the Al-4%Mg alloy is chosen as the master alloy. Through adding Ce and Nd as well as melting, casting and hot extrusion, the Al-Mg-RE alloys with different contents of Ce and Nd have been fabricated. The microstructural observations show that the addition of rare earth elements can refine the grains in the extruded Al-Mg-RE alloys, and the effect of the grain refinement is related to the adding content of rare earth element. In addition, it has been found that the addition of rare earth elements will result in the precipitation of secondary phase containing RE.
　　The results of tensile experiments reveal that the addition of Ce and Nd can significantly enhance the ultimate tensile strength and yield strength of the extruded Al-Mg-RE alloys. Especially when 0.5%Ce is added, the ultimate tensile strength of the alloy increases by 30.2%, and the yield strength increases by 47.9%. On the other hand, adding an appropriate content of Nd can increase the elongation of the extruded Al-Mg-RE alloy. When the adding content of Nd is 0.5%, the elongation to failure can be as high as 34%.The results of low-cyclic fatigue tests show that the addition of Ce and Nd can effectively enhance the fatigue lives of the extruded Al-Mg-RE alloys. During fatigue deformation, the extruded Al-Mg-RE alloys exhibit the cyclic strain hardening, softening and stable neodymium magnets cyclic stress response, which mainly depends on the imposed total strain as well as type and amount of the added RE elements. For the extruded Al-Mg-RE alloys, the relation between plastic and elastic strain amplitudes as well as reversals to failure can be described by Coffin-Manson and Basquin equations respectively. In addition, at the higher total strain amplitudes, a serrated flow can be observed in theσ-ε. hysteresis loop for the extruded Al-Mg-RE alloys. It means that the so-called dynamic strain aging takes place during fatigue deformation.The fractographic results reveal that under tensile loading http://www.chinamagnets.biz/ conditions, the extruded Al-Mg-RE alloys show typical ductile fracture, while under low-cycle fatigue loading conditions, the cracks initiate transgranularly at the surface of fatigue samples and propagate in a transgranular mode.