6061合金半固态电磁半连续铸造与模锻成型组织及性能研究

Microstructure and Mechanical Property of 6061 Alloy Near-Liquidus Electromagnetic Semi-Continuous Casting and Thixoforging

采用金相显微镜和电子拉伸机,研究了6061合金半固态坯料的电磁半连续铸造、二次加热、触变模锻成形以及成形件热处理。结果表明：采用近液相线电磁半连续铸造技术制备的6061合金半固态坯料微观组织为均匀、细小非枝晶组织;低过热度浇铸时,临界晶核半径减小,此时在电磁场作用下,降低了熔体的温度梯度,促进了准固相原子团簇在熔体中形成,形核率增大;二次加热时,初生α-Al不断球化,淬火组织也呈圆整状,620±5℃、保温15 min,模具温度250~300℃,留模时间10~15 s,触变成形出表面光洁的成形件;经T5处理后,抗拉强度达到328 MPa,延伸率达到8%,大大高于压铸成形件的性能。半固态压铸成形由于成形速度高,溶体高速充型,造成成形件气孔率高,使成形件组织致密度不如半固态模锻成形件,这是半固态压铸件强度低、模锻件强度高的主要原因。

The near-liquidus electromagnetic semi-continuous casting, remelting, thixoforging and heat treatment techniques of 6061 alloy were studied by means of metallographic microscope and electronic tensile machine. The results show that the semi-solid microstructure of the 6061 alloy prepared by the near-liquidus electromagnetic semi-continuous casting is uniform, fine and non-dendrite. When casting at the near-liquidus temperature, the radius of the critical nucleus decreases due to the temperature gradient decrease of the melt; at the same time, under the electromagnetic field, the formation of quasi-solid phase atom clusters is promoted, so the nucleation rate increases During remelting, the quenching microstructure is more spherical with the primary α-Al spheroidization. The optimum technique of semi-solid die-forging for 6061 alloy is as follows slurry temperature 620±5 ℃, heat preservation 15 min, die temperature 250 ℃-300 ℃, and holding time in die 10 -15 s. The ultimate tensile strength is 328 MPa and the elongation is 8% for the die forged alloy after T5 heat treatment, which are greatly higher than those of the die cast parts. The intensity of the die-cast alloy is lower than that of the forged because of fast forming speed, high pore content and low structure density.