Influence Of Melt Superheat Treatment On Melt Structure, Microstructure And Performance Of Directionally Solidified Al-Cu Alloy

Firstly, the physical models of Al-Cu based alloy melts were put forward through many experiments, and then the paper studied the influence of melt superheat treatment on Al-Cu alloy melt. Under the constant given conditions of technological parameters, as thermal gradient, withdraw velocity, etc; the influence of melt superheat treatment (including superheating temperature T_s, superheating time t_s, and low temperature holding time t_h) on the solidification microstructure and the primary dendrite arm spacing of directionally solidified Al-4.7%Cu alloy was studied. The stress-strain curves of directionally solidified specimens after different superheat treatment were measured by electronic universal material tester, their fracture morphology was analyzed by SEM and their crystal orientation was analyzed by XRD. We discussed the inner mechanism of the influence of melt superheat treatment on solidification structure, property and crystal orientation in order to enrich solidification theory and instruct practice.The result shows that the heterogeneous phenomenon of irreversible solid-like clusters, reversible solid-like clusters, reversible liquid-like clusters and short procedure may be present simultaneously in the Al-Cu alloy melts. The superheat treatment of Al-Cu alloy can make melt configuration state change irreversibly, the sensitive material property parameter such as viscous coefficient η and solute diffusion coefficient D_L shows hysteresis effect and crystallization undercooling â–³T. decreases. The melt superheat treatment can influence the directionally solidified structure and mechanical property obviously, the primary dendrite arm spacing λ₁ of the sample treated by superheat temperature 950℃ and 1050℃ decreases by more 30% than that of the sample treated by superheat temperature 750℃. The inactivation form of Al-4.7%Cu alloy sample that is not directional solidification is brittle fraction while that of directionally solidified Al-4.7%Cu alloy sample treated by different superheat treatment is tough fracture. The mechanics property of directionally solidified sample is better than that of none directionally solidified sample, the strength of the former increases by 60% and the elongation increases by nearly 100%. The directionally solidified Al-4.7%Cu alloy sample after treated by superheat treatment, its Cu-rich phase decreases obviously and its dimple number increasesobviously. The dendrites of Al-4.7%Cu alloy grow along with preferred orientation <100>. The diffraction intension of crystal face (100) lowers with the increase of superheat temperature, which shows that the branches of the crystal face orientation happen. The reason why superheat treatment can influence the microstructure, mechanics property and crystal orientation obviously is that superheat treatment changes the melt structure state and the change of the liquid metal structure is response to the influence.