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

1993 Fiscal Year Final Research Report Summary

• Project/Area Number: 04650634
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: 金属加工(含鋳造)
• Research Institution: Nihon University
• Principal Investigator: KANEKO Junichi Nihon Univ. Col. Indust. Tech., Professor, 生産工学部, 教授 (00120410)
• Project Period (FY): 1992 – 1993
• Keywords: Mechanical alloying / Powder metallurgy / Metal matrix composites / SiC whisker / Recrystallization / Crystallographic texture / Mechanical property / High temperature strength

Research Abstract

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.