回归再时效（RRA）处理对7050铝合金的影响

采用TEM和维氏硬度计研究了回归再时效 (RRA)处理对 70 5 0铝合金的影响 ,对处理后合金试样的强度和伸长率进行了测试 ,并对试样断口在SEM下进行了观察。研究发现 ,当回归温度为 45 3K ,在回归曲线上 ,随着回归时间的延长 ,硬度值下降 ,在 36 0 0s达到硬度最低值 ;继续延长回归时间 ,硬度值上升 ,在 72 0 0s硬度值达到最大值 ,随后硬度值下降 ;在RRA曲线上 ,随着回归时间的延长 ,硬度值上升 ,在 36 0 0s达到硬度峰 ,随后硬度值下降。当回归温度为 473K时 ,虽然与在 45 3K回归和再时效行为的趋势相同 ,但在回归曲线上 ,硬度的谷值和峰值时间都提前 ,并且硬度峰值稍微降低 ;在RRA曲线上 ,硬度峰提前。TEM研究结果表明 ,70 5 0铝合金在T6状态的硬化来自GP区。在回归处理过程中硬度谷值的产生与GP区的回溶有关 ,而峰值的产生与 η′和 η相的沉淀析出有关 ;在RRA处理过程中 ,峰值的产生与 η′和 η相的沉淀析出有关。回归温度对 70 5 0铝合金的影响与GP区、η′和 η相形核和时效沉淀动力学受回归温度影响有关。经过RRA(393K× 2 2h + 45 3K× 1h + 393K× 30h)处理后合金要比T745 1处理后的强度高 19% ,而伸长率稍微降低 ,经过RRA(393K× 2 2h + 473K× 5min + 393K× 30h)处理后合金要比T745 1处理后的强

Effect of RRA Treatment on Microstructures of 7050 Aluminium Alloy

Precipitation behavior of 7050 aluminium alloy has been studied by transmission electron microscopy and Vickers hardness tester after retrogression and reaging（RRA） treatment.The results indicate that，when the retrogression temperature was 453K，the value of hardness decreased firstly，and then reached a minimum value.With retrogression time increase，the hardness increased to form a hardness peak at the retrogression curve，and a hardness peak was observed on the RRA curve.When the regression temperature was 473 K，in comparison with retrogression at 453 K，the retrogression valley and peak promoted at the retrogression curve，and the hardness peak promoted at the RRA curve.TEM observation reveals that the effective hardness of the sample with T6 condition comes from GP zone.The dissolve of GP zone caused the decrease of hardness，and the precipitation of η and η′ caused the increase of hardness after retrogression.Analysis indicates that the precipitation kinetics of GP zone and η and η′ affected by temperature was reasonable for the different effect of retrogression and RRA． The ultimate tensile strength of the sample with RRA treatment （393K×22h＋453×K×1h＋393K×30h） was 19％ higher than that of the sample with T7451 treatment.In comparison with 453 K，the ultimate tensile strength of the sample with RRA treatment（393K×22h＋473K×5min＋393K×30h） was 16％ higher than that of the sample with T7451 treatment．The fracture surface was observed by SEM．It reveals that the fracture profiles are identified for samples at T7451 condition，453 K and 473 K RRA treatment.