Improving the formability of Mn-containing 6xxx Al alloys: role of additives and heat treatment

铝的最新开发工作集中在锻造合金上，其中通过使用成熟的Al挤压技术，诸如可热处理的6xxx系列合金的合金越来越多地用于片材和其他应用中，其中相对高的可成形性和使用强度是主要要求。Mg和Si是主要的合金元素，并且联合收割机形成Mg 2Si，即主要硬化相;通常添加Cu，以进一步提高强度。金属如Fe、Mn和Cr作为杂质或痕量添加物存在。因此，除了α-Al、Si和Mg 2Si之外，在合金的凝固、均匀化和热机械加工过程中还形成宽范围的含Fe和Cu的金属间化合物，即Al-Fe、Al-Fe-Si、Al-Fe-Mn-Si和Al-Mg-Si-Cu（Q相）。合金成分和铸造条件影响形成的金属间化合物的类型、形态和量，所施加的热处理也是如此。脆性β-Al 5 FeSi片晶对挤压性能产生不利影响，并在挤压材料中引起表面缺陷。因此，铸态合金在530- 600 ℃的温度下均匀化，在此期间，β-AlFeSi相转变为更有利的α-Al（FeMn）Si相，这显著改善了合金的可挤压性和表面质量。该项目建议通过选择合金成分和条件来研究6xxx合金中关键金属间相的形成，即Mg 2Si，β-Fe，α-Fe和含Cu的Q相，从而使每种金属间类型本身的形成变得简单。该研究将重点关注Mn（0.02-0.9%）在稳定β-到-α转变中的作用，以及添加剂如Zr和Sc以部分取代昂贵的Mn的作用，从而提供用于获得高合金成形性和增加的拉伸性能的具有成本效益的解决方案。硬度测量，拉伸性能和广泛的TEM和EPMA分析将被用来监测微观结构的演变，在铸态，均匀化，冷轧阶段，合金的可成形性。研究结果将有利于加拿大汽车和建筑行业，这是两个主要的应用领域。

Recent development efforts in aluminum have focused on wrought alloys where, through the use of the well-established technology of Al extrusions, such alloys as the heat-treatable 6xxx series alloys are being increasingly used in sheet and other applications where relatively high formability and in-service strength are major requirements. Mg and Si are the main alloying elements and combine to form Mg2Si, the primary hardening phase; Cu is commonly added, to further increase the strength. Metals such as Fe, Mn and Cr are present as impurities or trace additions. Thus, in addition to alpha-Al, Si and Mg2Si, a wide range of Fe and Cu-bearing intermetallics namely, Al-Fe, Al-Fe-Si, Al-Fe-Mn-Si and Al-Mg-Si-Cu (Q phase) form during solidification, homogenization and thermomechanical processing of the alloy. The alloy composition and casting conditions influence the type, morphology and amount of intermetallics formed, as do the thermal treatments applied. The brittle beta-Al5FeSi platelets adversely influence the extrusion properties and induce surface defects in the extruded material. The as-cast alloy is thus homogenized at temperatures of 530-600oC, during which the beta-AlFeSi phase transforms to the more favorable alpha-Al(FeMn)Si phase, which improves the alloy extrudability and surface quality considerably. This project proposes to study the formation of the key intermetallic phases, namely Mg2Si, beta-Fe, alpha-Fe, and the Cu-containing Q phase, occurring in 6xxx alloys by selecting alloy compositions and conditions favorizing the formation of each intermetallic type by itself. The study will focus on the role of Mn (0.02-0.9%) in stabilizing the beta-to-alpha transformation, and that of additions such as Zr and Sc to partially replace expensive Mn, and thus provide cost-effective solutions for attaining high alloy formability and increased tensile properties. Hardness measurements, tensile properties and extensive TEM and EPMA analyses will be used to monitor the microstructural evolution in the as-cast, homogenized, and cold rolled stages, in relation to alloy formability. The results would benefit the Canadian automotive and construction industries, two main application areas of interest.