Effect Of Sr On Mechanical Properties And Corrosion Resistance Of AZ81Magnesium Alloy

As an engineering material, magnesium alloys was used in industrial production for the first time until1886. Because of its high strength, low density, easy recycle, good damping, machinability and electromagnetic shielding property, magnesium alloys was known as’The21st century green engineering material’, and it had been widely used in Aerospace,3C electronic products and transportation, etc. The production was mainly casting, especially die casting. Because of its good room temperature-strength and corrosion resistance, etc, AZ91magnesium alloy was most wildly used in the casting magnesium alloy. But because its ductility was poor, and its strength was lower than aluminium alloy, enlarging its application fields is the key to develop magnesium alloys’ application right now. This thesis was aimed to improve the magnesium alloy materials comprehensive mechanical strength by alloying and heat treatment. Reducing the content of Al could improve the ductility and adding Sr as a metamorphic agent could refine grain, improve the microporosity of intergranular and interdendritic, at the same time raise its strength and ductility. The effects of Sr (0～0.9%) addition on the morphology of β-Mg17Al12phase, mechanical properties and Corrosion resistance were investigated by using metal mold casting forming process optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electronic tensile testing machine in this study.1) The Cast structure component phase of the test AZ81magnesium alloy contained primary a-Mg and divorced eutectic β-Mg17Al12phase, the morphology of β-Mg17Al12phase was continuously strip-like shape and discontinuously strip-like shape. With increasing of the Sr content, the morphology of β-Mg17Al12phase changed from continuously strip-like shape to discontinuously strip-like shape or particle-like shape, tended to discrete distribution and refined grain.β-Mg17Al12phase reduced and diffused further, grain reached the minimum, tensile strength (204MPa) and elongation (10.8%) reached the maximum with addition of0.6%Sr. As Sr content increases to0.9%, gram coarsening.2) After T6treatment, lamellar-like shapeβ-Mg17Al12phase was precipitated discontinuously, needle-like shape and point-like shapeβ-Mg17Al12phase was precipitated continuously. As a strengthening phase, P-Mg17Al12phase could effectively pinning dislocation, and improve tensile strength when the deformation, but at the same time β-Mgi7Al12phase was a hard-brittle phase to reduce the ductility. After T6treatment, the tensile strength of AZ81-0.6%Sr magnesium alloy reached240MPa, and elongation depress to8.0%. 3) Adding trace Sr (0.3%～0.6%) to AZ81magnesium alloy lead to reducing the corrosion potential, increasing corrosion current, so as to reduce the corrosion performance. But with Sr content increasing further (Sr content reach0.9%), the increasing of Al4Sr phase could raise the corrosion potential and improve the corrosion performance on the contrary.