| Magnesium alloy is not only low density but also has good conductivity, high specific strength, specific stiffness, high damping seismic, ease of casting and machining and also has many other excellent performance, so is known as the green environmental protection of metal structural materials in the 21st century. So many excellent properties of magnesium alloys makes it been widely used in the automotive, aerospace, automobile, the electronics industry. However, crystal structure of common magnesium and magnesium alloy is close the six-party structure (HCP), making the plastic forming ability poor. Besides, the high strength, heat resistance of magnesium alloy, the high manufacture cost of deformation magnesium alloy products, the corrosion resistance of and surface protection technology problems cause the application level of magnesium products is not high.The OM observation, SEM, EDS and XRD technology were employed for the analysis of microstructure, composition and phase distribution of the test alloy, and then explain the reasons of alloy mechanical properties change. The research mainly includes four parts:The influence of carbonate addition on the microstructure and mechanical properties of AZ91 magnesium alloy was studied in the first part. The results show that the average grain size of AZ91 alloy is refined from 245 um to 91 um and the tensile strength of AZ91 increases from 154 MPa to 179 MPa with addition of 0.6% manganese carbonate. The reasons of grain refinement are mainly due to the addition of manganese carbonate generating Al4C3 particles, which can be used as effective nucleation of primary α-Mg and reduce the grain size. And the mechanical properties of alloy are improved. Therefor, the manganese carbonate can be used as an effective grain refiner of magnesium alloys.The influence of Al-5Ti-0.2C addition and heat treatment on the microstructure and mechanical properties of AZ91 magnesium alloy was studied in the second part. The tensile strength of alloy reaches the optimal value of 170 MPa after adding 0.4% Al-5Ti-0.2C, the elongation is 10.16% at the same addition. The influence of Al-5Ti-0.2C addition on the microstructure and mechanical properties of AZ91(0.3%Mn) alloy was studied. After adding Al-5Ti-0.2C, the tensile strength of AZ91(0.3%Mn) increases from 149 MPa to 192MPa, yield strength of alloy increases from 94 MPa to 121 MPa, elongation of alloy increases from 1.19%to 8.15%, hardness of alloy increases from 62 HB to 84 HB. The influence of T6 heat treatment on the microstructure and mechanical properties of AZ91(0.3%Mn+0-0.8% Al-5Ti-0.2C) magnesium alloy was studied After solid solution and artificial aging treatment, tensile strength of alloy shows a trend of increasing, the peaked value is 205MPa with addition of 0.8% Al-5Ti-0.2C, yield strength of alloy is 133MPa with addition of 0.6% Al-5Ti-0.2C, the elongation of alloy is 7.77%. The highest hardness of the alloy is 104HB with addition of 0.8% Al-5Ti-0.2C.The influence of Cu addition and heat treatment on the microstructure and mechanical properties of AZ91 (0.3%Mn) was studied in the third part. The strength of alloy is 172 MPa with addition of 0.3% Cu. Yield strength of alloy achieves a peak of 116MPa, hardness of alloy increases to a maximum of 82 HB with Cu content of 1.0%.After solid solution treatment, the second phase dissolve into alloy and form single-phase supersaturated solid solution, network eutectic disappears. The grain boundary is clearly visible after corrosion. It is easy to see the change of the grain size. The results show addition of 0.5% Cu has made considerable grain refinement in AZ91 (0.3%Mn). After 22h artificial aging treatment of metal, the tensile strength of alloy with 0.5% Cu addition obtains the maximum value,240 MPa. The maximum hardness is 107 HB with addition of 0.5% Cu, the peak-aging time of alloy is 18 h. Compared to as-cast AZ91 (0.3%Mn) alloy, the hardness of alloy increases by 72.5%.The influence of Sn addition and heat treatment on the microstructure and mechanical properties of AZ91 (0.3%Mn) was studied in part four. With 0.5% Sn addition, tensile strength of alloy increases from 149MPa to 176MPa. Yield strength of alloy is 121MPa with 1.0% Sn addition. After adding Sn, hardness of alloy increases from 62HB to 62HB.After T6 heat treatment, tensile strength of alloy significantly increases from 185MPa to 228 MPa with the content of 0.5% Sn. Yield strength of alloy increases from 121MPa to 159MPa. The hardness of alloy obtains maximum,108HB after adding 0.5% Sn. In the process of aging, addition of Sn element can inhibits precipitation of discontinuous phase. |
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