Microstructure And Mechanical Behavior Of As-Extruded Magnesium And Aluminum Alloys

Both magnesium and aluminum alloys have such characteristics as low density, high specific strength and rigidity, and have found a wide application in aerocraft and automotive industries. Generally, magnesium and aluminum alloys are formed through hot extrusion in the manufacture of various structural components. It is obvious that the investigation concerning the microstructure and mechanical properties of as-extruded magnesium and aluminum alloys is of an important significance for the correct choice and use of these materials.In this investigation, the microstructure of two magnesium alloys including AZ91 and AM50, as well as three aluminum alloys including 6061,6063 and 3003 has been observed, and their mechanical properties at room temperature and elevated temperature have been examined, and the analysis on tensile fracture surfaces of these alloys has been carried out. Afterwards, the microstructure and mechanical properties of as-cast and extruded alloys is compared, and the influence of test temperature and heat treatment on the mechanical properties of as-extruded magnesium and aluminum alloys is investigated. At the same time, the fracture mode of these alloys during tensile deformation is also determined.The test results reveal that hot extrusion can effectively refine the microstructure of various magnesium and aluminum alloys, and thus enhance the mechanical properties of those alloys at room temperature. Compared with three aluminum alloys, the ultimate tensile and yield strength of two magnesium alloys can be more greatly enhanced after hot extrusion. For two magnesium alloys AZ91 and AM50 as well as the aluminum alloy 3003 subjected to hot extrusion, their ultimate tensile and yield strength increases with an increase in test temperature while their elongation to failure decreases with increasing test temperature. However, the tensile properties of the hot-extruded 6061 and 6063 aluminum alloys show a different tendence with changing test temperature. Aging treatment following hot extrusion can significantly increase the tensile properties at room temperature, as well as the ultimate tensile and yield strength at 200°C for the magnesium alloy AZ91. Solution treatment after hot extrusion can considerably enhance thetensile properties of the AZ91 alloy at room temperature at 150℃, as well as the elongation to failure at 200℃. The ultimate tensile and yield strength of the magnesium alloy AM50 at room temperature can be greatly increased through solution plus aging treatment after hot extrusion. Aging treatment following hot extrusion can significantly increase the ultimate tensile and yield strength at room temperature, as well as the ultimate tensile and yield strength at 150℃ and 200℃, as well as the elongation at different test temperatures for the AM50 alloy. The ultimate tensile and yield strength of the hot extruded aluminum alloy 6061 at various test temperatures is the highest among three aluminum alloys. For the aluminum alloy 3003 subjected to hot extrusion, its elongation at both 150℃ and 200℃ is the highest even though the elongation at room temperature is the lowest among three aluminum alloys. The SEM observations on the fracture surfaces of those tensile samples reveal that the AZ91 and AM50 alloys exhibit a mixed ductile and brittle fracture at room temperature while a ductile fracture mode can be noted at the higher temperatures. For three aluminum alloys subjected to hot extrusion, the ductile fracture occurs at various test temperatures used in this investigation.