Study On Microstructural Evolution Of Semi-Solid6063Aluminum Alloy In Recrystallization

Semisolid metal process has been paid much attention because of its fine characteristics such as high efficiency, high performance, low cost, energy conservation and environmental protection etc. The SSM had a large improvement on theory research and industrial application in the past40years. In order to achieve perfect semisolid billet microstructure, people have invented many techniques to make semisolid billet in the recently years, however, as a result of solidification latent heat in casting process, people could not achieve uniformity fine and spheroidal billet microstructure as expectation. Microstructure and capability of billet would be enhanced highly because of its fine grains after Thermomechanical treatment and it would reduce the technics demand of make semisolid slurry. In the aid of the National Natural Science Foundation of China, this paper choosed semisolid6063alloy as experimental material, studied the rule of the alloy microstructure evolution in recrystallization after Thermomechanical treatment. The main results achieved are as follows:The microstructure cold rolled to30%、40%、50%、60%、65%of alloy was studied, optical micrographs showed the grains of billet were staved after cold rolling, with the lager deformation degree, the grains microstructure would be staved more serious. When cold deformation degree reached50%, the grains microstructure after cold rolling would like flakes and some grains seemed like cracked rosebush, these cracked rosebush grains got togther like a strip, and its area would be increased with the larger deformation degree.The microstructure annealed at520℃and615℃for different time of alloy after cold rolling with reduction65%was studied, optical micrographs showed the grains size would be larger with the longer annealing time when alloy samples were annealed at520℃for5minutes to35minutes. While the grains size would be smaller with the shoter annealing time when annealed at615℃for lminute to5minutes.The microstructure annealed at520℃to625℃for5minutes of alloy after cold rolling with reduction65%was studied.optical micrographs showed the grains size would be larger with the higher annealing temperature. The spheroidal grains only appeared at from615℃to625℃.The microstructure annealed at one step high temperature for short time, two step low temperature for long time, and one step low temperature for long time, two step high temperature for short time of alloy after cold rolling with reduction60%was studied.optimal micrographs showed it can achieve perfect grain microstructure after one step high temperature for short time, two step low temperature for long time, The grain microstructure of alloy after one step low temperature for long time, two step high temperature for short time was grew up.In the paper, theoretical models for the recrystallization nucleation and growth were established concerning the Thermomechanical treatment. The models were used to predict the grains size in recrystallization. The theoretical models could explain the reasons why two-step recrystallization annealing wai better than one-step recrystallization annealing.This paper studied the rule of the alloy microstructure evolution for recrystallization after Thermomechanical treatment, achieved the technical processing parameters for the best grain microstructure, established recrystallization models for predicting grains size, explained physics mechanism and characteristic phenomenon during recrystallization treatment, supplied experimental foundation and theoretical database for improving semisolid billet microstructure.