热加工和后处理对Ti-6Al-4V合金显微组织和拉伸性能的影响

研究了热压缩、热轧制和后续轧制退火处理对Ti-6Al-4V合金显微组织和拉伸性能的影响。热压缩实验在温度800~1075°C和应变速率0.001~1s-1下进行,得到了流变曲线与加工过程参数之间的关系。然后,样品在温度800~1070°C和恒应变速率2s-1下进行2道次热轧制,总变形量为75%。热轧后,样品分别在870°C和920°C下保温热处理2h,随后空冷。在β相区的热轧导致粗大的β相冷却时转变为马氏体相,而在α/β两相区的热轧会导致生成部分球化的α相组织。后续的热轧处理能使在两相区部分球化的α相得以完成球化,然而,在β相区轧制的样品会导致马氏体结构被破坏。拉伸实验表明,随着轧制温度从两相区升高到单相区,合金的强度及伸长率会显著降低。升高热处理温度会降低两相区轧制合金的强度性能,而在β相区轧制合金的强度会得到提高。

Effect of hot working and post-deformation heat treatment on microstructure and tensile properties of Ti-6Al-4V alloy

The effects of hot compression, hot rolling and post-rolling annealing on microstructure and tensile properties of Ti-6Al-4V were analyzed. Hot compression tests were conducted in the temperature range of 800-1 075 °C and at strain rates of 0.001-1 s⁻¹, and the relations between the characteristic points of flow curve and processing variables were developed. Two passes of hot rolling test with total reduction of 75% were performed in the temperature range of 820-1 070 °C and at constant strain rate of 2 s⁻¹. After hot rolling, some specimens were subjected to heat treatment at 870 °C and 920 °C for 2 h followed by air cooling. Hot rolling in beta phase field resulted in coarse beta grains transforming to martensite by cooling. Otherwise, rolling in the alpha/beta phase filed gave rise to a partially globularized alpha microstructure. The post-rolling heat treatment completed the partial globularization of alpha phase in two-phase region and otherwise broke down the martensitic structure of beta-rolled samples. Tensile tests showed that the strength characteristics as well as elongation decrease significantly with increasing the rolling temperature from the two-phase to the single-phase region. Increasing heat treatment temperature contributed to lower strength for the specimens rolled in two-phase region and higher strength characteristics for the beta-rolled specimens.