Study Of The Microstructures And Properties In Al-2.99Cu-2.21Mg-0.48Si(Wt.%) Aluminium Alloy

The Al-Cu-Mg alloys are widely used as structural materials in military and civilian industries,significantly due to their high strength,especially superior creep strength at elevated temperatures.In order to fully dig the potential of Al-Cu-Mg alloy to meet the prformance requirements of materials in the aerospace field,it is common to add trace Si element to improve the comprehensive mechanical properties of the alloy,but it is still unclear how the precipiates behave and how to strengthen the matrix in Al-Cu-Mg-Si quaternary.The microstructure evolution and mechanical properties in Al-2.99Cu-2.21Mg-0.48Si(wt.%)alloy have been systematically investigated by scanning electron microscopy(SEM),electron back-scatter diffraction(EBSD),transmission electron microscopy(TEM),high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)analysis method and microhardness test,tensile test,corrosion(intergranular corrosion,peeling corrosion)test.The feasibility studies about improving the comprehensive performance,especially the corrosion resistance of Al-2.99Cu-2.21Mg-0.48 Si(wt.%)alloy by over-ageing treatment have been carried out via various corrosion test.The main results are as follows:(1)For the Al-2.99Cu-2.21Mg-0.48Si(wt.%)alloy aged at different temperature,there are primarily two kinds of hardening precipiate and their precursors,which are the S phase and GPB zones/Mg-Si cluster.The number of GPB zones/Mg-Si cluster can reach 93%in the peak-aging state and this GPB zones/Mg-Si cluster is the main strengthening phase,S phase as the secondary strengthening phase.It was found that the precipitates of under-aging are totally GPB zones/Mg-Si cluster,as the aging time increase,the number of GPB zones/Mg-Si cluster in the alloy decrease while the number of rod-like S phase increase,If the aging time is long enough,GPB zones/Mg-Si cluster will gradually disappear.(2)With 6%pre-deformed after the solution treatment,the comprehensive mechanics performance of the Al-2.99Cu-2.21Mg-0.48Si(wt.%)alloy decreased.The results show that the pre-deformation treatment introduces a large number of dislocations,which changes the precipition type of the alloy and inhibits the precipition of GPB zones/Mg-Si cluster.only the S phase as the strengthening precipition.Due to the large size and low density of the S phase,the mechanical properties decrease.(3)Al-2.99Cu-2.21Mg-0.48Si(wt.%)alloy introduced 6%pre-deformation can significantly improve the intergranular corrosion resistance of the alloy and through the combination with T7 treatment,the alloy has the better resistance to intergranular corrosion.The pre-deformation of the alloy has little effect on the exfoliation corrosion resistance aging at 180 ?,while the alloy with 6%pre-deformation can effectively improve the exfoliation corrosion resistance performance aging at 200 ?,and the combination of the over-aging treatment will reach better exfoliation corrosion resistance.