Role of heat treatment in optimizing microstructure of Al-Si cast alloys for elevated temperature applications

热处理在优化高温应用铝硅铸造合金微观结构中的作用

• 批准号: RGPIN-2020-07111
• 负责人: Samuel, Fawzy
• 金额: $ 2.4万
• 依托单位: École de technologie supérieure
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=754505
• 关键词: Role; heat; treatment; optimizing; microstructure

The properties of aluminum casting alloys are controlled by the microstructure which depends on the alloy composition and thermal conditions during solidification. The as-cast microstructure may be further altered if the casting is subjected to thermal exposure during a heat treatment process or when exposed to high temperature service conditions. In the latter case, minimum change in properties is desirable to maintain the performance and ensure sustainability of the component over its lifetime.   The majority of aluminum castings are derived from Al-Si based alloys, as silicon enhances the castability. The Si content controls the volume fraction of the eutectic Si phase formed in the alloy, which in turn constitutes a sizeable part of the microstructure, and thus influences the fracture behavior. While the eutectic Si phase has been studied over many years, its contribution to the elevated temperature properties when subjected to the high temperatures under actual service conditions is an aspect that has received little attention. It is important to explore this aspect in order to fully understand the elevated temperature behavior of Al-based alloys. In particular, it is important to determine how seriously the Si particle strength would be affected when the particles have undergone coarsening during thermal treatment. From recent studies, we have observed that the coarsened Si particles display certain defects like pinholes and grooves even after prolonged solution treatment times. However, the effect of these defects on the Si particle strength, premature failure and its consequences on casting quality has yet to be established. Besides using Al3X type dispersoids to maintain high temperature alloy strength, and controlling the negative effects of intermetallic phases, determining the optimum heat treatment parameters is crucial to promote maximum dissolution of strengthening Cu and Mg phases at the same time avoid incipient melting-related defects which would increase rejection rate and manufacturing costs. To stay ahead in the global market, Canada must place emphasis on high-quality products and lower production costs.   Thus, the research program will focus on the effects of Si particle coarsening on elevated temperature properties, using as examples 396 (11.5%Si), and 220 (1.2%Si) alloys recently developed for automotive applications, in addition to a low Mg-319 (6.5%Si) alloy for comparison. Both 220 and 396 alloys have the same level of Mg. Thus, the alloys cover Si content in the range 1.2-11% with two levels of Mg (~0.1, 0.35%) & Cu (~1.5, 4.5%). By carrying out a fundamental study of all aspects of enhancing the high temperature strength of these alloys, the main goal is to show how, through proper heat treatment, selection of alloy composition & additives, critical components with sustainable high temperature performance could be commercially produced at affordable cost, using such alloys to replace the currently used alloys.

铸造铝合金的性能受微观结构控制，而微观结构取决于合金成分和凝固过程中的热条件。如果铸件在热处理过程中或当暴露于高温使用条件时经受热暴露，则铸态微观结构可进一步改变。在后一种情况下，期望性能的最小变化以保持性能并确保部件在其寿命期间的可持续性。 大多数铝铸件都是由铝硅基合金制成的，因为硅提高了可铸性。Si含量控制合金中形成的共晶Si相的体积分数，共晶Si相又构成微观结构的相当大的部分，从而影响断裂行为。虽然共晶Si相已经被研究了很多年，但是当在实际使用条件下经受高温时，其对高温性能的贡献是很少受到关注的方面。为了全面了解铝基合金的高温行为，探索这方面的问题是很重要的。特别是，重要的是要确定如何严重的Si颗粒强度将受到影响时，颗粒在热处理过程中经历粗化。从最近的研究中，我们已经观察到，粗化的Si颗粒显示出某些缺陷，如针孔和凹槽，即使经过长时间的固溶处理时间。然而，这些缺陷对Si颗粒强度、过早失效及其对铸件质量的影响尚未确定。除了使用Al 3X型弥散体来保持高温合金强度和控制金属间相的负面影响之外，确定最佳热处理参数对于促进强化Cu和Mg相的最大溶解同时避免会增加废品率和制造成本的初始熔化相关缺陷至关重要。为了在全球市场保持领先地位，加拿大必须重视高质量的产品和降低生产成本。 因此，该研究计划将集中于Si颗粒粗化对高温性能的影响，除了用于比较的低Mg-319（6.5%Si）合金之外，还使用最近开发的用于汽车应用的396（11.5%Si）和220（1.2%Si）合金作为示例。220和396合金具有相同的Mg含量。因此，合金覆盖1.2-11%范围内的Si含量，具有两个水平的Mg（~0.1，0.35%）和Cu（~1.5，4.5%）。通过对提高这些合金高温强度的各个方面进行基础研究，主要目标是展示如何通过适当的热处理，选择合金成分和添加剂，以可承受的成本商业化生产具有可持续高温性能的关键部件，使用此类合金取代目前使用的合金。