Development of high-strength bolt material of Al-Mg-Si alloy by ECAP and various aging treatments

At present, the strength of most of Al-Mg-Si 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 Al-Mg- Si 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.