Dong Xixi, Amirkhanlou Sajjad, Ji Shouxun
Brunel Centre for Advanced Solidification Technology (BCAST), Institute of Materials and Manufacturing, Brunel University London, Uxbridge, UB8 3PH, United Kingdom.
Department of Materials, University of Oxford, Oxford, OX1 3PH, United Kingdom.
Sci Rep. 2019 Jul 3;9(1):9582. doi: 10.1038/s41598-019-46134-7.
Over the past several decades, it was generally believed that the strength of the industrially widely used cast Al-Si-Mg-Cu alloys enhanced monotonously with increasing Cu content. However, in this study using cast Al9Si0.5MgxCu (x = 0,0.2,0.4,0.6,0.85,1.0,1.25, in wt.%) alloys under T6 heat-treated condition, it was found that the hardness and yield strength of the heat-treated alloys showed a platform in the composition range from 0.4 wt.% to 0.85 wt.% Cu, while still increased with increasing Cu content before and after the platform. With increasing Cu content, the β-MgSi intermetallic phase decreased and disappeared at 0.85 wt.% Cu, while the Q-AlCuMgSi and θ-AlCu intermetallic phases increased in the as-cast alloys. After heat treatment, the micron-scale intermetallic phases were dissolved into the Al matrix and precipitated as the nanoscale β″, Q' and θ' strengthening phases. With increasing Cu content, the β″ precipitate decreased and vanished at 0.85 wt.% Cu, while the Q' and θ' precipitates increased in the heat-treated alloys. The trade-off of the phases induces the platform in the strength of the heat-treated alloys, and further increase of the Cu content in this undetected trapped platform range is not favorited industrially as it only decreases ductility.
在过去几十年里，人们普遍认为工业上广泛使用的铸造Al-Si-Mg-Cu合金的强度会随着铜含量的增加而单调增强。然而，在本研究中，使用在T6热处理条件下的铸造Al9Si0.5MgxCu（x = 0、0.2、0.4、0.6、0.85、1.0、1.25，重量百分比）合金，发现热处理合金的硬度和屈服强度在铜含量为0.4 wt.%至0.85 wt.%的范围内呈现出一个平台区，而在该平台区之前和之后，强度仍随铜含量的增加而提高。随着铜含量的增加，β-MgSi金属间相减少，并在铜含量为0.85 wt.%时消失，而铸态合金中的Q-AlCuMgSi和θ-AlCu金属间相增加。热处理后，微米级金属间相溶解到铝基体中，并沉淀为纳米级的β″、Q'和θ'强化相。随着铜含量的增加，β″析出相减少并在铜含量为0.85 wt.%时消失，而热处理合金中的Q'和θ'析出相增加。相之间的这种权衡导致了热处理合金强度出现平台区，并且在这个未检测到的被困平台区内进一步增加铜含量在工业上是不可取的，因为这只会降低延展性。
