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

高强度7075和2014铝合金的流变挤压工艺是利用其简单而独特的半固态浆料开发出来的，与触变挤压工艺相比，该工艺具有节能、低损耗等优点。首先，在Al-10%Mg和7075合金的触变挤压试验中，通过在模具前端进行适当的强制空气冷却，可以改善以相对较高的速度进行触变挤压的材料的低塑性(导致低强度)，然后在流变挤压的材料中也可能出现这种情况。作者使用一种由SUS直立细管和一定长度的倾斜水冷管组成的简单装置，制备了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，在强制高压下将熔体通过立管冷却到略高于液相线温度的条件下，可以获得含有平均直径小于50μm的固体颗粒的半固态浆料。将7075和2014合金的半固态浆料直接送入挤压容器中，在给定的温度、挤压比25：100和挤压速度5~20 mm/S下挤压成圆棒，可以比热挤压少几倍的力和一个数量级的速度得到良好的挤压。在含有最细固相颗粒的7075合金半固态浆料的使用中，560℃、挤压比36、拉速10 mm/S的棒材具有与热挤压相当的良好的拉伸伸长率、强度和时效硬化性能。

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.