Effects Of Microcontent Sr On The Microstructures And Properties Of AZ80 Wrought Magnesium Alloy

Magnesium alloys, as light structural materials, have many special advantages, such as low density, high specific strength, high specific stiffness, good casting capability, electromagnetic shielding performance and easy reclamation etc. So magnesium alloys are extensively used in automobiles, airplanes, computers, communication equipments and etc. They are known as 'the green project materials having development potential and best future in the 21st century'. But because magnesium has hcp crystal structure, slip system is little, plastic deformation is hard. Excluding cast, very few available manufacturing methods can be adopted. The application of magnesium alloys is still confined. Potential should be fully rooted. To develop magnesium alloys has important significance on continuous development of social economy.In this paper, AZ80 based alloys was chosen, the effects of microcontent Sr on microstructure and properties of AZ80 wrought alloys at as-cast state, hot-extruding state and re-extruding state were studied with OM, XRD, DSC, SEM, EDS, corrosion potential testing and mechanical properties testing. The results show that at the as-cast state, main phases in the alloys are α-Mg and β-Mg₁₇Al₁₂ phase. The alloys with 0.02% and 0.16% Sr 3^# alloys have no other phase compared with 1^# alloy with original composition of AZ80 alloy. The phase, Mg₁₇Sr₂ is found in 4^# alloy with 0.30% Sr. The grains are refined apparently with adding microcontent Sr and become smaller and smaller with the increase of Sr, phases in the boundaries become thicker and net-structure is formed. Sr is almost gathered in the boundaries and Mn, Zn and Al are mainly also in the boundaries by the analysis of plane distribution. Sr possibly has two styles in the as-cast alloys. On one hand, Sr solid-solutes into the alloys to affect Mg₁₇Al₁₂ phase and refine the alloys as the active surface element, on the other hand, Sr forms high-temperature stable Mg₁₇Sr₂ phase with Mg. The formed phase is high-temperature stable phase to improve the eutectic temperature and refine the grains. The tensile strength(UTS)and elongation of the three alloys with Sr are higher compared with the alloy without Sr. The UTS and the elongation of three alloys with Sr are improved 20²5MPa and 40¹00% respectively at as-cast state.After preliminary hot-extruding(Extrusion ratio λ=3.6), main phases are still a-Mg matrix and β-Mg₁₇Al₁₂ phase. The grains are refined to different degree. Dynamic secrystallization(DRX) has happened, DRX of the alloys with Sr is completed relatively and the structure is more homogeneous. Extrusion orientation in the alloys with Sr is not as clear as AZ80 alloy. But mixed structure of original grains and recrystallizing grains is...