Effect Of Heat Treatments On Mechanical Properties Of Exruded Mg-Al-Ni(-RE) Alloys

Wrought magnesium alloys usually exhibit the higher strength and plasticity than cast magnesium alloys. Furthermore, for wrought magnesium alloys, the higher strength, better ductility and multiplex mechanical properties can be achieved through controlling their microstructures and adopting appropriate heat treatment technology in order to meet the need of more components and extend the application fields of magnesium alloys. Thus, wrought magnesium alloys show much more significant potential in further applications of magnesium based materials.The Mg-Al-Ni(-RE) alloys were fabricated by melting, casting and hot extruding. The heat treatments including single aging, double aging and solid solution plus aging were performed for some extruded Mg-Al-Ni(-RE) alloys. The influence of heat treatment on microstructure, mechanical property and fracture behavior of the extruded Mg-Al-Ni(-RE) alloys was studied through microstructural observations, tensile experiments and analysis of fracture surfaces.The microstructural observations reveal that the strengthening phase particles precipitate at grain boundaries and inside grains for the extruded Mg-Al-Ni(-RE) alloys subjected to single and double aging treatments. The microstructure of the alloy gets refined after single aging treatment, and becomes coarse after double aging and solid solution plus aging treatments.The results of tensile experiments show that the single aging treatment can increase the elongation at various temperatures as well as ultimate tensile strength and yield strength at room temperature for the extruded Mg-Al-Ni(-RE) alloys, and significantly increases the elongation of the extruded Mg-6%Al-0.5%Ni-0.5%Ce alloy. The double aging treatment can effectively enhance the ultimate tensile strength and yield strength of the extruded Mg-Al-Ni(-RE) alloys at high temperature. Although the solid solution plus aging treatment can increase the elongation of the extruded Mg-6%Al-0.5%Ni-0.5%Ce alloy at room temperature, but decrease the elongation of the extruded Mg-6%Al-0.5%Ni- 0.5%Ce alloy at high temperature as well as the ultimate tensile strength and yield strength of the alloy at various temperatures.The fractographic analysis reveal that the extruded Mg-6%A1 and Mg-6%Al-0.5%Ni -0.5%Ce alloys shows typical ductile fractured, but the extruded Mg-6%Al-0.5%Ni alloy shows the mixed ductile and brittle fracture. The extruded Mg-Al-Ni(-RE) alloys subjected to single aging treatment show the mixed ductile at room temperature and 150℃, while exhibit the typical ductile fracture at 200℃. The extruded Mg-Al-Ni(-RE) alloys subjected to double aging treatment basically show the mixed ductile and brittle fracture.