Grain Refinement Effect And Refinement Mechanism Of The Industrial Electrolyzed Al-Based Alloy And The Alloy's Application

The preliminary experiment and the following six-month-long experiment of producing the Al-based alloys with low titanium contents in the industrial electrolyzer are carried out in this paper. The grain refinement effects of these alloy produced by electrolysis are comparably investigated with that of pure aluminum refined with the ordinary master alloy. The formation and growth of the equi-axed grain are studied, and the grain refinement mechanism of the Al-based alloy is discussed. The Al-based alloy is used as the starting material for producing a series of Al-Si alloys and a series of Al-Cu alloys, and the influences of silicon and copper contents on the grain refinement effects are comparably investigated. The influences of melting time, solute element content and aging procedure on the properties of the A356 alloy made from the Al-based alloy are preliminarily studied.A series of Al-based alloys with low titanium contents are producing in the industrial self-baking electrolyzer with the current intensity of 42 KA, and the Al-based alloys with titanium contents of 0.1-0.2 % are produced for about 6 months in the pre-baked electrolyzer with the current intensity of 80 KA. The industrial experiments results show that it is feasible to produce the Al-based alloy with low titanium by addition of TiO2 powders into the ordinary cryolite-alumina melts in the suitable addition manner. The industrial electrolyzer can work in the ordinary order, and the technical parameters of electrolyzer, such as the temperature of cryolite-alumina etc. remain stable, and the current efficiency and output of aluminum etc. are just the same as that of industrial production of pure aluminum.The influences of titanium contents on the macro-grain grades, the micro-grain sizes and grain morphologies of the Al-based alloys ingots and the samples after being re-melted for several times are investigated, and the grain refinement of the pure aluminum refined with the master alloy with the corresponding addition is comparably studied. The grain refining results show that the Al based alloys can obtain the favorite grain refinement, and the variety of grain size is smaller than that of pure aluminum refined with the master alloy. The fine and even equi-axed grains are revealed in the Al-based alloys, and this favorite grain refinement remains stable even after the alloy has been re-melted for more than 4 times. Producing the Al-based alloy in the ordinary electrolyzer is a simple and efficient refining route of aluminum alloy, and can be put into industrial production.The nucleation and growth behavior of equi-axed grain in the Al-based alloy is firstly investigated under SEM, and the mechanism of grain refinement is studied in view of equi-axed formation behavior and the heat-flow environment. The atoms of titanium are quickly entered into and distributed uniformly among the aluminum melts during the electrolyzing. In the following solidification, the fine particles containing titanium are firstly precipitated from the aluminum melts with titanium content more than 0.12 %, and distributed evenly among the aluminum melts. When the temperature falls down to the crystallization temperature of a -Al, some potential particles will be activated as the nucleates of a -Al crystals by the under-cooling, in the same time the solute titanium is segregated and the constitutional under-cooling occurs ahead the growing solid/liquid interface. The sufficient constitutional under-cooling is both necessary for the potential particles to be activated as the nucleants of a -Al, and for the a -Al crystals to grow as the equi-axed morphology in the suitable environment. Titanium segregation and nucleation can cooperate and occur ahead the growing interface. The cyclical mechanism produces a wave of equi-axed grains advancing toward the center of the melts. The sufficient under-cooling due to solute titanium segregation and the even potential nucleants ensure the Al-based alloys revealing in the fine equi-axed grains. Besides the potential TiAls parti...