Study On Microstructure Refinement Of Weld Metal And Property Of HAZ For High Strength Al-Cu Alloy

Al-Cu alloy is widely used in aeronautical and space aerocraft light armor vehicle and some parts of automobile owing to its excellent high temperature and super-low temperature mechanical properties. It is necessary to continue to research its weldability because the investigation on the weldability of Al-Cu alloy is few at present .This paper aimed at the problem in welding the middle thick Al-Cu alloy plate ,such as low weld metal strength HAZ softening, the measures to resolve them were put forward.The microstructure of weld metal was refined and the strength of weld was improved by the inoculants Zr and Ti in filler wires increasing the effective nucleation particles of weld and adopting synergic pulsed MIG welding process. The results showed that the weld solidification structures consisted of the fine equixed grains with additions of 0.31%Zr and 0.26Ti in filler wires and the mechanical properties of the weld joint were increased greatly. The low-frequency pulse frequency , low-frequency pulse time and the peak voltage difference between low-frequency pulse and high-frequency pulse were chosen as the orthogonal experiment parameters of synergic pulsed MIG welding process. The conclusion was drawn that when high-frequency pulse parameters were not changed the low-frequency pulse parameters were respectively: pulse time 3ms pulse frequency 6Hz and peak voltage difference 3V,the amount of dendrite structures was increased in weld metals. The strength and plasticity of weld metal were improved.The softening reasons of various areas in HAZ were investigated by thermal simulation technology. The exsolution aggregation and growth of strengthening phases in HAZ were the main reasons of HAZ softening. The weld joints were heat treated respectively by artificial ageing and solid-solution + artificial ageing treat. The results showed that the strengtheningaction of aging treatment in 160℃ × 16h was better than180℃ × 16h, but the strengthening action of solid-solution and artificial ageing (the parameter 530℃ ×2.5h+160℃ × 16h) was best.