Grain Refinement of Aluminum Alloy Bar by a Modified RAP Process for Semi-Solid Forming

摘要

A modified Recrystallization and Partial Melting (RAP) process including Radial Forging (RF) and Semi-Solid Isothermal Treatment (SSIT) was proposed to refine the grains of 6063 Al alloy bar for semi-solid forming. The 6063 Al alloy bar (phi 120 mmfixfi800 mm) was deformed by RF into a stepped shaft with different Area Reduction Ratios (ARRs) at the temperature of 300 degrees C, and then the samples cut from both the central and peripheral parts of the RF-deformed bar were treated with SSIT at 630 degrees C for 10 min. The effect of ARR on the microstructural evolution of semi-solid 6063 Al alloy was investigated. Results showed that, during the RF process, the microstructures of the samples became denser as the ARR increased. After SSIT, with the increase of ARR, the average grain sizes of both the central and peripheral parts were reduced and the spheroidization degrees of both the central and peripheral parts were improved. The variation tendency of grain size experienced three different stages: precipitous reduction, gentle reduction and unobvious change. Besides, the differences between grain sizes of the peripheral and central parts were gradually decreased with the increase of ARR. Additionally, the optimal process parameter for refining grains was 70% ARR at 630 degrees C for 10 min.