Rheo-extrusion of high-strength aluminum alloys using semi-solid slurry made by solidification-rate controlling technique

利用7075和2014高强度铝合金的半固态浆料，尝试开发一种简单而独特的流变挤压工艺，与触敏挤压工艺相比，该工艺具有节能、低损耗等优点。首先，在Al-10%Mg合金和7075合金的触模挤压试验中，在较高速度下的触模挤压材料中出现的低延性（导致低强度），以及在流变挤压材料中可能出现的低延性（导致低强度），可以通过在模出口前位置进行适当的强制空气冷却来改善。作者使用了一种简单的装置，由一根薄薄的SUS直立管和一根一定长度的倾斜水冷管组成，制作了2014和7075合金的半固态浆料。经过多次试验，特别是在后一种合金中，在强制高压下，将经垂直管冷却至略高于液相温度的熔体送入水冷管的条件下，可以得到含固体颗粒的平均粒径小于50μm的半固态浆料。将平均固体颗粒直径在110 ~ 50μm之间的7075和2014合金的半固态浆料直接引入挤压容器中，然后在给定温度、挤压比25 ~ 100、冲压速度5 ~ 20mm/s的条件下挤压成圆棒。与热挤压相比，用小几倍的力和快一个数量级的速度就能很好地挤压它们。在含有最细固体颗粒的7075合金半固态浆料中，在560℃、挤压比为36、挤压速度为10mm/s条件下流变挤压的棒材具有良好的拉伸伸长率、强度和时效硬化性，与热挤压棒材相当。

Rheo-extrusion process of high strength 7075 and 2014 aluminum alloys has been tried to develop utilizing their semi-solid slurries made by an easy and unique method, because this process has some great advantages such as saving energies and low lost in contrast to the thixo-extrution process. At first, low ductility (resulted in low strength), which occurs in the materials thixo-extruded at relatively higher speeds and then may also be caused in rheo-extruded ones, could be improved by an adequate forced-air cooling at forward position of die out-let in the thixo-extrusion tests using Al-10%Mg and 7075 alloys. The author used a simple device made of a thin SUS upright tube followed by a certain length of inclined water-cooled tube to make semi-solid slurries of 2014 and 7075 alloys. After many trials, especially in the latter alloy, semi-solid slurries containing solid particles with mean diameter of less than 50μm could be obtained under the condition feeding the melt, which had been cooled to slightly above liquidus temperature by passing down through the upright tube, into the water-cooled tube at forced high pressure. Semi-solid slurries of 7075 and 2014 alloys with various mean diameters of solid particles ranging 110 to 50μm were directly introduced within an extrusion container and then extruded to round bars at given temperatures, extrusion ratios of 25 to 100 and ram speeds of 5 to 20mm/s. They could be extruded soundly at a few times less force and faster by an order of magnitude than those of hot-extrusion. In the usages of 7075 alloy semi-solid slurries containing the finest solid particles, the bars rheo-extruded at 560℃, extrusion ratio of 36 and ram speed of 10mm/s showed the favorable tensile elongation, strength and age-hardenability equivalent to those of hot-extruded one.