Improvement of high temperature strength of MA Al and Cu P/M materials by directional annealing

通过热挤压，机械合金化P/M铝材料和晶须增强铝合金复合材料的基体中普遍形成细晶粒组织。在这种情况下，由于晶粒晶界滑动的增加，高温下抗拉强度降低，伸长率显著增加。在极端情况下观察到超塑性。虽然这些特性适用于这些高级材料的热加工，但在其最终用途中，需要在高温下具有更高的强度。本研究将定向退火技术应用于MA P/M铝材料和SiC/6061挤压复合材料，目的是通过使基体晶粒粗化来提高高温强度。在MA定向退火过程中，基体晶粒未发生明显的粗化，MA引入的分散颗粒稳定了基体的细晶结构。而在873K下定向退火5h， SiCw/6061挤压复合材料出现明显的软化。在定向退火和挤压状态下，6061合金基体的织构均<111>。得到的退火材料的极点图明显显示出基体的粗大晶粒结构。在673K时，定向退火材料的抗拉强度高于挤压态材料。然而，室温下的拉伸强度通过定向退火降低了50 ~ 100mpa。因此，热挤压形成的基体的细晶粒和亚晶粒结构有助于复合材料在室温下的明显强度增加。综上所述，SiCw/6061挤压复合材料的定向退火可以在牺牲室温强度的前提下提高高温强度。

By hot extrusion, fine grained microstructures are generally formed in the matrix of mechanically alloyed P/M aluminum materiaaaaaaaaals and whisker reinforced aluminum alloy composites. in such cases, tensile strength decreases and elongation increases markedly at high temperatures due to increased contribution of grain grain boundary sliding. Superplasticity is observed in the extreme. Although such properties are suitable for hot working of these advanced mateerials, much higher strength at elevated temperates is desirable at their end uses. in this work, directional annealing was applied to MA P/M aluminum materials and SiC/6061 extruded composites for the purpose of attaining improved high temperature strength by causing grain coarsening of the matrix.No appreciable grain coarsening of the matrix was observed in directional annealing of MA P/M aluminum materials, in which the fine graind structure was stabilized by finely dispersed particles introduced by MA.However, directional annealing at 873K for 5h caused appreciable softening of SiCw/6061 extruded composites. the pole figures showed the <111> texture of the 6061 alloy matrix for both as-extruded and directionally annealed materials. The obtaind pole figures of the annealed materials obviously showed coarse grain structures of the matrix. At 673K, the directionally annealed materials showed higher tensile strength than as-extruded ones. However, tensile strengt at room temperature is decreased by 50 to 100 MPa by applying directional annealing. Thus, fine grain and subgrain structures of the matrix formed by hot extrusion are contributing to an appreciable strength increment of the composites at room temperature. In conclusion, directional annealing of SiCw/6061 extruded composites can give improved high-temperature strength at the sacrifice of room-teemperature strength.