Ultrafine-grained Al–5 wt.% Fe alloy processed by ECAP with backpressure

Abstract

A process for increasing both strength and ductility in a brittle Al–5 wt.% Fe alloy by Equal Channel Angular Pressing (ECAP) was investigated. The increase in solid solubility of iron in the Al matrix produced by intense deformation under ECAP permitted age hardening in this alloy although it is not hardenable by conventional processing. An ultrafine-grained microstructure of 325–450 nm was obtained in a brittle, cast Al–5 wt.% Fe alloy by ECAP with various numbers of passes and backpressure levels from 40 to 275 MPa. A supersaturated solid solution with a maximum solubility of 0.6 wt.% of iron in an aluminium matrix was obtained during ECAP, which allowed ageing of the conventionally non-hardenable alloy. Strength, ductility and microhardness of the cast alloy processed by the ECAP technique were significantly enhanced (e.g. strength and ductility from 102 MPa and 3.4% to 261 MPa and 5.8%, respectively). The subsequent artificial ageing resulted in a further increase in strength to 272 MPa. It was shown by scanning electron microscopy (SEM) that the type of fracture of tensile specimens taken from material subjected to ECAP was predominantly ductile. An increase in backpressure retards cracking of intermetallic particles and enhances the workability and ductility of such alloys processed by ECAP.