Papers by Keyword: Mg₂Si Phase

Abstract: The microstructure and hardness of as-cast Mg-5Si-7Sn-5Mn alloy after solution and ageing treatments is presented in this paper. It was found that the microstructure of as-cast alloy. is composed of primary dendrites crystals of Mg₂Si phase, α-Mg matrix, long needle-like precipitates of Mn₅Si₃, Chinese script particles of Mg₂Si phase and irregular Mg₂Sn phase. The solution treatment at 500°C causes the dissolution of the Mg₂Sn phase in the α-Mg magnesium solid solution, whereas the remaining intermetallic compounds are stable in this temperature. The hardness of alloy increases from 73 HV2 to 96 HV2 at 250°C. The increase in hardness is a result of the formation of the lath-like precipitates of Mg₂Sn phase within the α-Mg matrix.

Abstract: The microstructure of Mg-5Si alloy consists of the primary coarse Mg₂Si phase, α-Mg solid solution and eutectic α-Mg + Mg₂Si, in which eutectic Mg₂Si phase solidifies in the form of Chinese script particles. When 0.2 wt.% of Ca was added to the Mg-5Si alloy the size of primary Mg₂Si phase remained unchanged. The modification effect of calcium on the primary Mg₂Si phase was effective only in the Mg-5Si-0.5Ca alloy. The morphology of the primary Mg₂Si phase is changed from the coarse dendrite shape to polyhedral shape and the size of primary crystals is significantly reduced. The addition of 0.6 wt.% Ca to Mg-7Si alloy did not cause the modification of primary Mg₂Si phase.

Abstract: The Mg-6Zn-2Si alloy was processed by equal channel angular pressing (ECAP) for 4 passes and 8 passes at 573K, and the microstructure and mechanical properties of the alloy before and after ECAP were studied. The results show that Chinese script type interphase of Mg₂Si was crushed into dispersed particles, and significant grain refinement was also introduced to the matrix phase (α-Mg) and Mg₅₁Zn₂₀ phase after 4 passes of ECAP. The yield strength was increased by 180%, elongation by 140% and tensile strength by 75%. The microstructure and mechanical properties remained reasonably constant between 4 and 8 passes of ECAP. The mechanism of improvement on microstructure and mechanical properties of the experimental alloy by subjecting ECAP was also investigated.

Abstract: The microstructure and mechanical properties of AZ61-4Si magnesium alloy before and after equal channel angular processing (ECAP) were studied. Results show that the matrix α-Mg and divorced eutectic β-Mg₁₇Al₁₂ are refined and chinese script type Mg₂Si phases are broken to dispersed particles after ECAP. The mechanical properties of the alloy after ECAP are significantly improved. After 4 passes of ECAP, the yield strength is increased from 50MPa to 109 MPa, tensile strength from 129MPa to 237MPa, elongation from 6% to 22%, and hardness from 61.2HBS to71.5HBS. The modification mechanism for microstructure and mechanical properties of the experimental alloy by ECAP was analyzed.

Abstract: In this paper, the effects of Sb addition on heat-treated microstructure and mechanical properties of AZ61-0.7Si magnesium alloy were investigated. The results indicate that the solution heat treatment can modify the Chinese script shaped Mg2Si phase in the AZ61-0.7Si alloy. After solutionized at 420°C, the morphology of the Mg2Si phase in the AZ61-0.7Si alloy changes from the Chinese script shape to the short pole and block shapes, and the higher modification efficiency could be obtained for the alloy with the addition of 0.4 wt.%Sb. In addition, the effect of the solution heat treatment on the morphology of the Mg2Si phase can also result in the improvement of tensile and creep properties for the AZ61-0.7Si alloy. After solutionized at 420°C for 24h and followed by aging treatment at 200°C for 12h, the AZ61-0.7Si alloy exhibits higher tensile and creep properties than that of the as-cast alloy, and the properties improvement resulted from heat treatment, is more obvious for the AZ61-0.7Si alloy with the addition of 0.4 wt.%Sb.

Abstract: In this paper, the effects of Sb and RE on the solutionized microstructure and microhardness of Mg-6A1-1Zn-0.7Si magnesium alloy are investigated. The research results indicate that the solid solution treatment can result to the modification of Chinese script shaped Mg2Si phases in the microstructure of experimental alloy, and adding small amounts of RE and Sb can strengthen the modification efficiency. In addition, after the solid solution treatment at 420°C, the Mg-6A1-1Zn-0.7Si alloy added 0.4%Sb and 0.25%RE exhibits higher microhardness, but the effect of Sb and RE additions on the changing law between microhardness and solutionized time, is not obvious.

Abstract: The effects of the Al content on the as-cast microstructure and mechanical properties of Mg-xAl-0.7Si based magnesium alloys which contained 1%Zn, 0.25%Mn, 0.4%Sb and 0.25%RE were investigated by optical microscopy(OM), scanning electron microscopy(SEM), X-ray diffraction(XRD) analysis and tensile testing. The results indicated that the effects of the Al content from 6% to 8% on the alloy phase types of the experimental alloys were not obvious, and the as-cast microstructure of the experimental alloys with different Al content were composed mainly of the α-Mg matrix, Mg17Al12 phase, Mg2Si phase and Mg3Sb2 phase. The Chinese script morphology of the Mg2Si phase was very obvious in the experimental alloy with 6%Al. With the increase of Al content from 6% to 8%, the yield strength of the experimental Mg-xA1-0.7Si based alloys at room temperature increased, but the yield strength of the experimental Mg-xA1-0.7Si based alloys at 150 °C decreased.