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

• Published in: Journal of Japan Institute of Light Metals Vol. 68; no. 2; pp. 65 - 72
• Main Authors: Iwaoka, Hideaki, Hirosawa, Shoichi, Mouri, Keiki, Obata, Tomoyasu, Shimoda, Masahiko, Tang, Yongpeng
• Format: Journal Article
• Language: Japanese
• Published: Tokyo The Japan Institute of Light Metals 2018; Japan Science and Technology Agency
• Subjects: Aging (artificial); aging treatment; Aluminum base alloys; Al–Mg–Si; ECAP; Elongation; Equal channel angular pressing; High strength alloys; High strength bolts; high-strength bolt; Magnesium; mechanical properties; Room temperature; Silicon; Ultimate tensile strength
• ISSN: 0451-5994; 1880-8018
• DOI: 10.2464/jilm.68.65

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.