6082铝合金CCT图的测定及应用

DETERMINATION AND APPLICATION OF CCT DIAGRAM FOR 6082 ALUMINUM ALLOY

采用动态电阻法测得6082铝合金连续冷却过程的电阻-温度曲线,根据曲线斜率变化判断相变点及临界冷却速率,绘制出该合金的连续冷却转变曲线(CCT图),通过TEM对组织转变的观察验证了所测CCT图,模拟实际生产条件对CCT图进行应用研究.结果表明,动态电阻法测得的CCT图是可信的;随着冷却速率的增加,相变开始温度先降低,在达到某冷却速率时骤升,然后继续降低;相变主要集中在220—400℃的温度区间发生,抑制相变发生的临界冷却速率在16—34℃/s之间;20mm厚实验合金板适宜采用60℃水淬,淬火转移时间较长,利用所测CCT图可以制定分级淬火工艺,从而在最大限度减小淬火应力的同时抑制平衡相的析出.

Electrical resistance-temperature curves of 6082 aluminum alloy at various cooling rates during continuous cooling was obtained by in-situ resistance measurement.Phase transformation start and finish temperatures were ascertained by the slope change of resistance-temperature curves. Continuous cooling transformation（CCT） diagram for 6082 aluminum alloy was plotted.Microstructure evolution during cooling was examined by TEM observation to verify the validity of the CCT diagram.Applications of the CCT diagram were studied in this work.The results show that the CCT diagram obtained by in situ resistance measurement is credible.Resistance-temperature curves corresponding to different cooling rates depart from straight line to different directions.The phase transformation start and finish temperature decreases with the increase of cooling rates when the cooling rate is slow,but as the cooling rate increases to a certain rate the phase transformation start temperature increases suddenly and then decreases continously.Phase transformations mainly take place between 220 and 400℃.Critical cooling rate for preventing phase transformation is between 16—34℃/s.For plates 20 mm in thickness is proper to quench by 60℃water.A step-quench process can be established by the tested CCT diagram to decrease quenching stress utmost and inhibit equilibrium phase precipitation at the same time.