变形程度对7A04合金半固态触变组织的影响

Effect of Effective Strain on Semi-solid Thixotropic Microstructure of 7A04 Alloy

获得具有触变特性的均匀的、近球形的显微组织是半固态触变成形工艺的基础和关键。以挤压态7A04合金SIMA法生成触变组织为例,研究变形程度对其半固态触变组织的影响。结果表明:在加热前的变形程度对显微组织的影响很大,随着变形程度的增加,晶粒尺寸减小,晶粒形状越趋于球形;当变形程度超过0.3时,晶粒尺寸及其球形化速度逐渐减慢并趋于稳定值。此外,经过冷变形后,晶粒内及晶粒间的偏析减小,晶界易被低熔点液相浸润,更易获得均匀的、近球形的触变组织。

Obtaining uniform and globular microstructure becomes the basis and key to whole semi-solid metal forming.The commercial 7A04 alloy as-extrusion was employed as raw material, and SIMA method （strain induced melting activety） was used to obtain semi-solid billet. The effect of effective strain on thixotropic microstructure was studied. The results show that effective strain in cold deformation before reheating has a great influence on microstructural evolution. Grain size decreases and its shape also approaches to sphericity with the increase of effective strain. When effective strain exceeds 0.3, the grain size and its sphericizing speed decrease slowly and approach to a steady value. Moreover, after cold deformation, the segregation between grains decreases, eutectic liquid easily fills into all grain boundaries, so uniform and globular microstructure is obtained more easily.