Influence Of Yb Addition On Microstructures And Corrosion Resistance Properties Of Aluminum Alloy2519A

The aluminum alloy2519A samples with different Yb additions (0,0.2%,0.3%,0.4%) were prepared by ingot metallurgy method, and the influence of Yb addition on microstructures and corrosion resistance properties of aluminum alloy2519A was investigated by vickers hardness test, tensile test, tafel polarization curve test, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy(TEM). Meantime, the effects of two-step ageing treatment on microstructures and properties of aluminum alloy2519A was studied. Main conclusions are listed in the following:(1) The effects of rare earth elements Yb on microstructures of2519A aluminum alloy were obtained. The results show that the addition of0.2%Yb can decrease the number of coarse second phases. Aslo, the0’phase can be refined and its area fraction increased. As a result, the continuous precipitation of θ(Al2Cu) phase at the grain boundaries can be prevented, and it can make the precipitation at the grain boundaries become discontinuous and reduce the width of PFZ(precipitation free zone) size at the grain boundaries. Meanwhile, the results show that0.2%Yb addition can decrease the corrosion current and corrosion speed of aluminum alloy2519A. So the mechanical properties and corrosion resistance properties of2519A alloy plate can be improved. But more Yb contents lead to no futher increasing of the mechanical and corrosion resistance properties. The number of coarse second phases increased and the area fraction of θ’ phase become more smaller. Morever, the precipitation at the grain boundaries become continuous and the width of PFZ size increased. Aslo, the corrosion current become stronger.(2) The best addition of Yb in2519A alloy is0.2%. Which lead to the optimized properties and corrosion resistance properties. Compared with2519A alloy, the ultimate tensile strength of rare earth containing alloys increases from483.4MPa to509.3MPa, The maximum depth of intergranular corrosion and stress corrosion index are reduced from142.9μm to117.7μm and0.03326to0.02531, respectively. Also, the exfoliation corrosion grade is cut down.(3) The influence of two-step ageing treatment on microstructures and properties of aluminum alloy2519A containing Yb were investigated. Compared with2519A alloy treated by single-stage ageing, the two-step aging process improves the corrosion resistance, but decreases the mechanical properties. The intergranular corrosion grade of alloy plates, which Yb content is0.2%,0.3%,0.4%, all descend from4to3, and the exfoliation corrosion degree is also fallen down.(4) Compared with2519A alloy containing Yb treated by single-stage ageing, the precipitates at grain boundaries reduced and their size become more coarser after two-step ageing, which also make precipitation at the grain boundaries become discontinuous. However, because there are coarse precipitates containing Yb, and the affinity between Yb and H is strong. So the tendency of hydrogen bubble rupture become larger. As a result, the corrosion speed becomes fast at the beginning, which may make corrosion current of the alloys stronger in tafel polarization curve test.