PDF《7A04 铝合金连续冷却转变曲线的测定》

第20 卷第

4 期 中国有色金属学报

2010 年4月Vol.

20 No.4 The Chinese Journal of Nonferrous Metals Apr.

2010 文章编号:1004-0609(2010)04-0640-07 7A04 铝合金连续冷却转变曲线的测定 李红英 1,2 ,王晓峰

1 ,唐宜1,邓云

1 ,黄愉1,孙 远1,王法云

1 (1. 中南大学 材料科学与工程学院,长沙 410083;

2. 中南大学 有色金属材料科学与工程教育部重点实验室,长沙 410083) 摘要:对7A04 铝合金固溶处理后的连续冷却转变(CCT 图)进行测定.通过动态电阻法测得冷却过程的电阻― 温度曲线,根据曲线斜率的变化规律确定相变开始点、结束点以及临界冷却速度所处范围,绘制该合金的 CCT 图,利用扫描电镜和 X 射线衍射分析观察连续冷却过程中合金的组织转变.结果表明:电阻对连续冷却过程的组 织变化敏感,动态电阻法测得的 CCT 图是可信的;

经470℃、1 h 固溶处理后,抑制相变发生的临界冷却速度低 于35.37 /s ℃ , 但高于 9.96 /s ℃ ;

随着冷却速度的增加, 相变开始温度和结束温度均降低, 相变主要集中在 150~400 ℃的温度区间发生;

快速冷却时,合金保持较高的过饱和度,在60 ℃以下仍有相变发生,慢速冷却时,MgZn2 平衡相在晶内和晶界大量析出并逐渐长大和粗化. 关键字:7A04 铝合金;

CCT 图;

动态电阻;

相变 中图分类号:TG

151 文献标志码:A Measurement of continuous cooling transformation curves of 7A04 aluminum alloy LI Hong-ying1,

2 , WANG Xiao-feng1 , TANG Yi1 , DENG Yun-zhe1 , HUANG Yu1 , SUN Yuan1 , WANG Fa-yun1 (1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;

2. Key Laboratory of Nonferrous Metals Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, China) Abstract: The continuous cooling transformation (CCT) curves of aluminum alloy 7A04 were measured. The electrical resistance―temperature curves during the continuous cooling processes were obtained by in-situ resistance measurement. The starting and finishing temperatures of the phase transformation and critical cooling rate range were established by analyzing the slope change of the obtained curves, and then CCT curves were drawn. The microstructure evolution of the alloy during cooling process was observed by SEM and XRD. The results show that the electrical resistivity of the sample is sensitive to the microstructure change produced by continuous cooling transformation, and the CCT curves obtained by in-situ resistance measurement are credible. After solution treated at

470 ℃ for

1 h the critical cooling rate to prevent the phase transformation of the samples is above 9.96 /s but below 35.37 ℃ /s, ℃ the phase transformation starting and finishing temperatures decrease with increasing cooling rates and it mainly happens in the temperature range of 150?400 . High speed cooling leads to high concentration of solute thus ℃ the phase reaction happens even below

60 , ℃ and low speed cooling brings precipitation, growth and coarsening of MgZn2 equilibrium phase in the grains and at the grain boundaries. Key words: 7A04 aluminum alloy;

continuous cooling transformation curves;

in-situ electrical resistance;

phase transformation 铝合金的热处理强化效果与淬火速率密切相关, 提高淬火冷却速度通常会使合金强度提高[1?4] .但是, 对于大尺寸及形状复杂的构件,较大的淬火速率容易 导致残余应力过大,因此,合理控制淬火冷却速度十 收稿日期:2009-02-18;