Influence Of Mg Content On The Aging Precipitation Behavior And Property Of Al-3.5Cu-xMg Alloy

Abstract:Mg element affects the aging precipitation behavior and the property of Al-Cu-Mg alloy as the main alloying element. This article selects Al-3.5Cu-xMg alloy as the research object, and the range of Mg content is from0.71%to1.85%. The influence of Mg content on the property and aging precipitation behavior were investigated by Optical Microscopy (OM), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), High Resolution Electron Microscopy (HREM) study. According to the experimental data under different aging treatment condition, the main conclusions are as follows:(1) The heat treatment systems of Al-3.5Cu-xMg alloys were explored. The reasonable homogenization, solution and peak aging treatment are heating up to490℃during12h and keeping warm for24h under490℃,510℃/2h,185℃/12h respectively. There are three aging curves with different shapes under170℃,185℃,200℃. However, Mg content doesn’t have a significant affect on the time to achieve peak-values for the Al-3.5Cu-xMg alloys.(2) The peak artificial aging precipitation behavior and property of Al-3.5Cu-xMg-alloys were revealed. Firstly, with the increase of Mg content, the hardness and strength of Al-3.5Cu-xMg alloys improve, but the elongation goes down. Moreover, the degree of improvement becomes small with the increase of Mg content. When Mg content increases from0.71%to1.3%, the main precipitates are transformed from S+θ’+Ω phases to S phases which results in the increase of hardness and strength. When Mg content rises from1.3%to1.85%, the increase of hardness and strength is caused by the increase of the main precipitates. Secondly, as Mg content increased, the fracture toughness and exfoliation corrosion resistance of Al-3.5Cu-xMg alloys tend to decrease. Because the PFZ zones of Al-3.5Cu-xMg alloys widen and there is a more centralized precipitates in Al-3.5Cu-xMg alloys. Finally, Ω-phase is found in Al-3.48Cu-0.71Mg for the first time. The Cu/Mg ratio of Al-Cu-Mg alloys which have the precipitation of Ω-phase during traditional heat treatment process reduces to4.9.(3) The peak double creep aging precipitation behavior and property of Al-3.5Cu-xMg alloys were explored. Firstly, with the increase of Mg contents, the strength of Al-3.5Cu-xMg increases, but the fracture toughness decreases. However, compared with the Al-3.5Cu-xMg in artificial aging, the strength of Al-3.5Cu-xMg in double creep aging rises slightly, the fracture toughness rises significantly, and the main precipitates don’t change. Secondly, compared with the2124alloy, the strengths of Al-3.5Cu-xMg alloys decrease slightly, but the fracture toughness improves significantly. This result indicates that the fracture toughness improves significantly when Cu content of Al-Cu-Mg alloys reduces appropriately.