非等温回归再时效对7055铝合金中厚板的厚向组织及性能均匀性的影响

Effect of non-isothermal retrogression and re-ageing on through-thickness homogeneity of microstructure and properties in 7055 aluminum alloy medium thick plate

通过力学性能测试、腐蚀性能测试、透射电镜(TEM)观察和动力学计算研究回归加热、冷却速率的匹配对回归再时效(RRA)态7055铝合金中厚板析出组织均匀性及厚向性能的影响。结果表明:固定回归加热速率,合金的强度、断裂韧性和耐腐蚀性能的均匀性及厚向析出组织的均匀性随着回归冷却速率的降低而提高。但是慢速回归降温增加合金析出相的粗化程度,导致合金强度下降。综合考虑性能及均匀性,建立的包含空冷降温处理以补偿7055铝合金中厚板厚向组织均匀性的"非等温回归再时效"制度为(105℃,24 h)+(190℃,70 min)(升温速率3℃/min,70 min包含加热时间)+(空冷25 min至120℃)+(120℃,24 h)。经非等温回归再时效处理后,7055铝合金板材心层的抗拉强度、断裂韧性及剥落腐蚀等级分别为619 MPa、24.7 MPa?m1/2和EB-,其强度的厚向均匀性比常规回归再时效处理的提高约50%。

The effect of matching relationship between retrogression heating and cooling rate on the microstructure homogeneity and through-thickness properties of medium-thick 7055 aluminum alloy plate was investigated by mechanical properties test, corrosion resistance test, transmission electron microscope(TEM) observation and kinetics calculation. The results show that, the through-thickness of strength, fracture toughness, corrosion resistance and microstructure homogeneity increase with the decrease of retrogression cooling rate when heating rate is fixed. However, the slow retrogression cooling rate increases the coarsening degree of precipitates, which results in the deterioration of strength. Considering the compositive request to properties and homogeneity, the “non-isothermal retrogression and re-ageing” temper based on the air cooling treatment to through-thickness homogeneity was established as (105℃, 24 h)+(190℃, 70 min) (heating rate 3℃/min, 70 min including heating time)+(air cooling 25 min to 120℃)+( 120℃, 24 h). After “non-isothermal retrogression and re-ageing” treated, the tensile strength, fracture toughness and exfoliation corrosion resistance level are 619 MPa, 24.7 MPa?m1/2 and EB?, respectively. The through-thickness homogeneity of strength increases by 50% when compared to that of the conventional RRA treatment.