半固态2A12铝合金部分重熔组织的演变

Microstructural Evolution of 2A12 Aluminum Alloy Prepared by Low Voltage Pulsed Magnetic Field Process during Partial Remelting

对低压脉冲磁场技术制备的2A12铝合金半固态坯料进行部分重熔,利用光学显微镜和图像分析仪等,对半固态坯料部分重熔微观组织的演变进行了研究。结果表明,随着加热温度的提高或保温时间的延长,坯料的平均晶粒尺寸增大,重熔液相增加,晶粒的圆整度提高。最佳的部分重熔工艺参数如下:加热温度为620℃左右,保温时间为20～40min。形成初生α-Al晶粒为均匀的近球形颗粒,平均晶粒尺寸为116～120μm,液相率在40%左右,适合于半固态触变成形。组织演化机制分析表明,部分重熔的初期阶段,重熔液相较少,晶粒主要通过凝并快速长大;随加热温度的升高和保温时间的延长,重熔液相增加,晶粒主要通过原子扩散慢速长大并发生球化。

The semi-solid 2A12 aluminum alloy prepared by low voltage pulsed magnetic field process was partially remelted, and its microstructural evolution was observed by means of optical microscope and graphical analyzer. The experimental results show that the a-A1 grains are coarsened gradually and become more globular with the increase of the isothermal temperature and holding time. For the 2A12 aluminum alloy, primary a-A1 grains exhibit uniformly near spherical structure with size of 116～120 μm, and liquid phase fraction is approximately 40% at 620 ℃ for 20～40 min, suitable for semi-solid thixoforming. It is found that in the early stage of the whole partial remelting process, the volume fraction of liquid is low and grains are grown up fastly mainly through crashing and fusing, while grains are grown up slowly and spheroidized mainly through elements diffusion as a result of increasing in volume fraction of liquid phase with the increase of the isothermal temperature and holding time.