| Abstract:Microalloying is an importent method of improving comprehensive performance or a particular performance for aluminum alloys. This article selects Al-3.5Cu-1.5Mg alloy(Cu/Mg atom ratio0.9) as the research object, using Optical Microscopy (OM),Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), High Resolution Electron Microscopy (HREM), to study the influence of Li/Zr/Sc addition on the property and aging precipitation behavior. According to the experimental data in different aging treatment condition, the main conclusions are as follows:(1) Aging precipitation behavior of Al-3.5Cu-1.5Mg-1.0(Li) alloy at185℃was revealed. The addition of lithium (1.0%) delays the alloy peak aging time, postpones the formationcan of S’(Al2CuMg) phase. Meanwhile, the precipitation of the Al-3.5Cu-1.5Mg alloy changes from S’(Al2CuMg) phase to S’(Al2CuMg) and δ’(Al3Li) phases. Lithium addition makes Precipitation Free Zone (PFZ) narrowed.(2) The evolution of properties of Al-3.5Cu-1.5Mg-(1.0Li) alloy during aging was explored. Lithium increases the yield strength by29MPa at peaking aging condition. The tensile strength is improved by21MPa. However, the elongation of the alloy decreases from20.3%to15.8%, still keeping good plasticity. Peaking aging tear strength of Al-3.5Cu-1.5Mg alloy increased, but the crack Initiation Energy per Unit area (UIE) is reduced and anisotropy is enhanced. The form of fracture morphology is changed from ductile fracture to ductile/brittle mixed fracture.(3) The corrosion resistance of these alloys at different aging time was revealed. InAl-3.5Cu-1.5Mg alloy, exfoliation corrosion performance of185℃aging for24h is the worst. The performance at peaking aging is worse than that at36h overaging. In Al-3.5Cu-1.5Mg-1.0Li alloy, this performance at185℃peak aging (24h) is worst, overaging (36h) is worse, and underaging is the best. Coarsening rate of Grain Boundary Precipitation (GBP) is declined.(4) The influence of Zr/Sc complex addition on the aging precipitation and performance of Al-3.5Cu-1.5Mg-1.0Li alloy was preliminarily explored. The influence of Zr/Sc composite addition on Al-3.5Cu-1.5Mg-1.0Li alloy aging time in different temperature (170℃/185℃/200℃) is small. When aging at185℃,the peak aging hardness, tensile strength, yield strength,UIE are improved, however elongation, TS value is reduced, anisotropy are reduced. Zr/Sc composite addition makes the subgrain spilling more difficult. The main aging precipitation of alloy is not changed. The number of transgranular fracture at tensile testing is bigger. |
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