Development of high-strength bolt material of AlMgSi alloy by ECAP and various aging treatments

Abstract

At present, the strength of most of AlMgSi alloy bolts is not enough, and thus highly expected to be increased, for example, to >500 MPa in ultimate tensile strength (UTS). In this study, mechanical strength of A6056 AlMgSi alloy was aimed at improving, without diminishing the elongation, by combined application of equal-channel angular pressing (ECAP) and various aging treatments. Multi-pass ECAP and pre-aging (PA) treatment at 373 K for 1.2 ks was found to be effective in strengthening the bolt material subject to room-temperature storage followed by artificial aging. Especially, PA plus ECAP 2pass treatment exerted the biggest impact on the strength (i.e. 514 MPa in UTS) with a reasonable elongation to fracture (i.e. 16%). Such a high strength and good ductility exceeds minimum requirement for aluminum-made bolts registered in JIS B1057, and thus the developed PA-ECAP 2pass specimen can be utilized potentially as a high-strength bolt material.