【摘要】 为探讨改善Mg-Al合金耐热性能的途径,开发性能优良、价格廉价的镁合金,采用硅合金化的方法,研究不同硅含量时Mg-9%Al-x%Si合金(x=3,6和9)的凝固组织和室温力学性能。结果表明,三种铸态合金均由-αMg相、Mg2Si和-βMg17Al12组成。Mg2Si呈树枝状,且随硅含量提高,枝晶越发达,体积分数也增大。随Si量的增多,合金的抗拉强度、屈服强度和伸长率下降,硬度提高。经过415℃×12h固溶处理后,Mg2Si相的尖角钝化,部分Mg2Si相呈形状规整的椭圆形。固溶处理使Mg-9%Al-6%Si合金的抗拉强度和伸长率提高,时效可提高合金强度和硬度。Mg2Si相固液界面生长前沿的溶质边界层造成的成分过冷区及生长晶面上不同地方之间硅元素过饱和度的差异造成Mg2Si晶体凝固界面失稳,从而使得本属于小晶面生长的Mg2Si相在实际生长条件下为枝晶生长方式。更多还原

【Abstract】 In order to probe into the approach to improve heat resistance of Mg-Al based alloys,effect of silicon on microstructure and mechanical properties of graphite mould cast Mg-9%Al-x%Si（x=3,6 and 9） alloys was examined.The microstructure of the alloys consists of α-Mg,dendrite Mg₂Si and β-Mg₁₇Al₁₂ phases.The size and volume fraction of dendrite Mg₂Si phase increase with the increase of silicon content.Tensile strength,yield strength and elongation of the alloys decrease and hardness increases as silicon content increases.After solution treatment at 415℃ for 12 hours,the sharp tips of Mg₂Si phases in the alloys become rounded,and some elliptic Mg₂Si phases appears.Solution treatment can simutaniusly improve tensile strength and elongation of the Mg-9%Al-6%Si alloy,and its strength and hardness can be increased further by ageing.The solid-liquid interface is faceted when Mg₂Si phase grows under equilibrium condition.The Al-rich solute boundary layer formed in front of solid-liquid interface in the melt when Mg₂Si crystals grow under practical conditions results in formation of the constitutional supercooling region.Meanwhile,the degree of supersaturation of silicon at different places on a crystal plane of Mg₂Si phase is different.These make the planar growth of Mg₂Si phase is not stable,and as a result,the growth mode of Mg₂Si phase changes to dendritic growth when the dimension of Mg₂Si phase is large enough.更多还原