Study On Microstructures And Properties Of Rapidly Solidified AlFe VSi Heat-Resistant Aluminum Alloy And Preparation Techniques Of Its Large-Size Products

Rapidly solidified high temperature aluminum alloy is a kind of lightweight structural materials with high specific strength, high specific stiffness and good heat-resistance. It is able to be applied at the temperature range of 150-350C (and even higher temperature ) instead of some of titanium alloys or steels, to meet the need of advanced space shuttle, aircrafts and missiles to high flying velocity and large carrying capacity in the modern space-flight and aviation industries. In the past the high temperature aluminum alloy was prepared by using rapid solidincation (including melt atomization and planar flow casting)-powder metallurgical technology. However, in the preparation of large scale structural materials, spray deposition processes integrate advantages of rapidly solidification, semi-solid forming and near-net shape forming technology, and thus over several years a lot of attention were focused on the novel near-net shape blank-making process with good potential application. Spray deposition process may be used to develop large-scale structural materials of the rapidly solidified heat-resistant aluminum alloy, substituting for rapidly solidification-powder metallurgical processes.In this dissertation development and status quo of rapidly solidified heat-resistant aluminum alloy, rapid solidification-powder metallurgical technology and spray deposition processes are commented. Aiming at some abnormal phenomena found in the investigation of rapidly so lidified AlFeVSi alloy, and so me main problem that need to solve in the preparation of high performance large scale structural materials of spray deposited AlFeVSi alloy, comparing with rapidly solidified powder metallurgical AlFeVSi alloy, the following researches were done,Microstructures and mechanical properties of spray deposited AlFeVSi alloy blank and its formed produces were investigated. The results show that, spray deposited AlFeVSi alloy blank exhibits inhomogeneous structural character on the micro scale, but high performance rapidly solidified AlFeVSi alloy may be prepared by using this kind of spray deposited blank.Coarsening behavior of Al12(Fe,V)3Si particles in the rapidly solidified AlFeVSi alloy and its microstructural thermal stabilities during thermal exposure at high temperature were investigated. The results show t hat, W hen i s r apidly solidified A lFeVSi a Hoy e xposed t hermally a t high t emperature, main c hange below 500Cin the alloy is Ostwald ripening of Al12(Fe,V)3Si particle, and above 550'C, Al12(Fe,V)3Si will congregate along grain boundaries, and even appear needle-shaped or clumpish -Al13Fe4 phase. In addition, abnormal multiplication of dislocation occur in the rapidly solidified AlFeVSi alloy, accompanying particle coarsening and grain growing. Coarsening behavior of Al12(Fe,V)3Si particle in the rapidly solidified AlFeVSi alloy is in obedience to prediction of the modified Lifshitz-Slyozov-Wagner (LSW) particle ripening theory. Its coarsening rate is dependent on bulk diffusion of iron atoms and diffusion of iron atoms along interface in the a-Al matrix. In the temperature range of 420~520C, coarsening rate of Al12(Fe,V)3Si particle is very low, its magnitude being 10-24~10-26 m3 h-1, mean activation energy of diffusion, QEXP=208kJ mol-1, is between activation energy of bulk diffusion of iron atoms, Qdiff =259kJmor', and activation energy of diffusion of iron atoms along interface, Qinter=146kJ mol-1.Plastic deformation behavior of spray deposited AlFeVSi alloy at various temperatures was investigated. The results show that, rapidly solidified AlFeVSi alloy has low strain hardening coefficient, and even exhibits work softening, and has a drop of ductility at intermediate temperature 100-300C). Aiming at high temperature plastic deformation of spray deposited AlFeVSi alloy, phenomenological constitutive relationship based on Zener-Hollomon parameter method and physical constitutive relationship based on Rosler-Artz model are established. The R-A physical model can give a good prediction for the abnormal behavi...