Glass-Fibre-Reinforced Aluminium Alloys Formed by Hot Extrusion: Part II: Heat-Treatment

Abstract

The microstructures of rapidly solidified 7050 alloy powders have been observed by optical microscopy, scanning electron microscopy, and transmission electron microscopy and compared with those observed in a cast and homogenized ingot of the same material. The powder alloy was then consolidated by cold compaction followed by extrusion, the resulting structures being compared with those of extruded cast alloys. Finally, the structure and properties of the two materials were compared after heat treatment. It is shown that metastable phases not previously reported are present in the powder particles and that localized melting occurs in the powder alloy at a lower temperature than in the cast alloy; this is the primary cause of blistering, but appropriate modification to the heat treatment will prevent it occurring. Properties comparable to or better than the cast material may be produced by designing a more suitable heat treatment to avoid liquation of this metastable phase. The evidence presented suggests that the degassing procedure employed historically to counteract blistering is probably unnecessary. PM/0322