Effects Of Strontium And Silicon On Microstructures And Heat Resistance Of Magnesium Alloy

In this paper, Mg-25%Sr master alloy was added in the hypereutectic Mg-Si alloy for modification。The hypereutectic Mg-4%Si alloy was modified by adding alkaline-earth element Sr to Mg-25% Sr master alloy. The effect of Sr addition on the modification of the primary Mg2 Si phases and the influence of Sr and Si on the properties of Mg-Si alloy were investigated. Mg-Si-Sr alloy were fabricated via flux protection and gas protection methods, and part of the materials fabricated by gas were extruded.Mg-Si-Sr alloy microstructures were investigated by optical microscope(OM), scanning electronic microscope and electron probe microanalysis(EPMA). Phase analysis of the alloy materials were studied by X-ray diffraction analysis(XRD). The hardness of alloy materials was tested by using Vickers hardness tester. Thermal expansion properties and high-temperature tensile properties of the alloy were tested by using dilatometer and thermal simulation testing machine respectively.The results showed that the alkaline-earth element Sr can effectively metamorphose the primary Mg2 Si on hypereutectic Mg-Si alloy. The primary Mg2 Si size decreased significantly(average size from 50μm to 20μm), Its shape from coarse dendrite, non regular shape particles as the shape changes relatively regular particles. The shape of eutectic Mg2 Si changed from significant Chinese character into fine short rod.The addition of Sr to the Mg-4%Si alloy can cause that the alloy primary Mg2 Si size decreased significantly and reduced the hardness of the alloy; As for the magnesium alloy with different Si content, the hardness increased with the increase of silicon content. The dimensional stability of Mg-4Si-1Sr alloy improved a lot after 24 hours of incubation at 400℃. d L/L0(20-400℃)value decreased from 10-2 to 8×10-3. Alloy material prepared by gravity casting had more defects, so the tensile strength can only reach 105 MPa, at 150℃ and 0.05 strain rate condition. After extrusion, the alloy material defects significantly reduced, at a strain rate of 0.05 and 150 ℃ conditions, the tensile strength can reach 139 MPa.