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Influence of magnesium content on the mechanical properties of cast hypereutectic aluminum-silicon alloys.

机译：镁含量对铸造过共晶铝硅合金力学性能的影响。

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摘要

The current study focuses on the influence of the Mg content on the mechanical properties of cast hypereutectic Al-Si alloys. With increasing the Mg content, the formation of the primary Mg2Si tends to substitute for the primary Si progressively in the modified castings with the properties close to the Si crystals, both of which are believed to be important in Al alloys. Other than the Al-Si alloy system has been fully developed, the Al-Mg 2Si composites however just start to be concerned recently. A new alloy system is thus established based on the conventional cast hypereutectic Al-Si A390 alloy with increasing Mg content. The formation of the primary Mg 2Si is the main characteristic of adding Mg into the alloy A390, tending to substitute for the primary Si progressively. Equilibrium calculations and binary/ ternary/ quaternary phase diagram plots were carried out using the FactSage(TM) software, predicting the Al-Si alloy system alternatives with the Mg additions. The 6 and 10 wt% Mg alloys were found to be representative of the different decomposition behaviours in two transition regions where both primary phases can be precipitated in a particular order of Si to Mg 2Si for the alloy with lower magnesium content and Mg2Si to Si for the second composition. For both alloys, the Mg2Si phase is significant in the aluminum matrix.The T6 heat treatments of these new alloys increased the mechanical properties with respect to their as cast condition but smaller than the increment measured from the alloy A390. One of reasons might be relates to the heat treatments while another could be associated with the high level casting flaws, including the porosities and oxidation products that were encountered when casting these alloys. Further investigation of the microstructures showed that increased Mg additions favour the defect formation and reduce the castability. The tensile fracture analysis indicates most cracks were initiated by these porosities or oxidation products in the castings resulting in brittle fracture. This limits the application of the permanent mould castings for these new alloys even though weight reductions can be achieved 2.6% for the 6 wt% alloy and 4.9% for the 10 wt% alloy when compared to the conventional A390 alloy. However, this further can be improved by introducing die casting or semi-solid forming.Permanent mould castings were produced of these two alloy compositions, and further tested for their hardness and tensile properties in comparison with the conventional A390 alloy. T6 heat treatment and Bi modifications of these two alloy compositions were also tested. The preliminary results denote that their hardness was increased somewhat with Mg additions due to the solid solution strengthening mechanism, while the yield strength and elastic modulus exhibited only a slight difference with respect to A390, whereas ultimate tensile strength was lower for the new alloys. The structure modifications due to Bi additions (0.6~0.8 wt%) to the 6 wt% Mg alloy show an overall improvement of the mechanical properties. It was observed that the snowflake-shaped Bi-bearing phases segregating at the primary Mg2Si solidifying fronts, thus refining Mg2Si crystals.
机译：当前的研究集中在镁含量对铸造过共晶铝硅合金力学性能的影响。随着Mg含量的增加，初生Mg2Si的形成倾向于在改性铸件中逐步替代初生Si，其性能接近于Si晶体，这两者在铝合金中都被认为很重要。除了已经充分开发了Al-Si合金系统以外，Al-Mg 2Si复合材料最近才开始受到关注。因此，基于具有增加的Mg含量的常规铸造过共晶Al-Si A390合金建立了新的合金系统。初生Mg 2Si的形成是向合金A390中添加Mg的主要特征，倾向于逐步替代初生Si。使用FactSage™软件进行平衡计算和二元/三元/四元相图，预测添加Mg的Al-Si合金系统的替代方案。发现镁含量为6wt％和10wt％的Mg合金代表了两个过渡区域中不同的分解行为，对于镁含量较低的合金，Mg2Si相对于Si的合金，两个初生相都可以以Si到Mg 2Si的特定顺序析出。第二种成分。对于这两种合金，Mg2Si相在铝基体中都非常重要。这些新合金的T6热处理提高了铸造状态下的机械性能，但小于从A390合金测得的增量。原因之一可能与热处理有关，而另一原因可能与高水平的铸造缺陷有关，包括铸造这些合金时遇到的孔隙和氧化产物。对微观结构的进一步研究表明，增加的Mg添加有利于缺陷的形成并降低可铸性。拉伸断裂分析表明，大多数裂纹是由这些孔隙或铸件中的氧化产物引起的，从而导致脆性断裂。即使与传统的A390合金相比，重量减轻了6％（重量）的合金达到2.6％，重量减轻了10％（重量）的4.9％，这也限制了永久铸模在这些新合金中的应用。然而，这可以通过引入压铸或半固态成形而得到进一步改善。由这两种合金成分制成的永久铸件，并与常规A390合金相比，进一步测试了它们的硬度和拉伸性能。还测试了这两种合金成分的T6热处理和Bi改性。初步结果表明，由于固溶强化机制，添加了Mg后其硬度有所提高，而屈服强度和弹性模量与A390相比仅表现出细微的差异，而新合金的极限拉伸强度却较低。由于向6 wt％的Mg合金中添加Bi（0.6〜0.8 wt％）而导致的结构改性显示出整体机械性能的改善。观察到，雪花形的含Bi相在主要的Mg2Si凝固前沿偏析，从而细化了Mg2Si晶体。

著录项

  • 作者

    Liu, Xichun.;

  • 作者单位

    Ecole Polytechnique, Montreal (Canada).;

  • 授予单位 Ecole Polytechnique, Montreal (Canada).;
  • 学科 Engineering Chemical.Engineering Materials Science.Engineering Metallurgy.
  • 学位 M.Sc.A.
  • 年度 2010
  • 页码 221 p.
  • 总页数 221
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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