High-strength bolt-forming of fine-grained aluminum alloy 6061 with a continuous hybrid process

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 552; pp. 316 - 322
• Main Authors: Kim, Ji Hun, Hwang, Sun Kwang, Im, Yong-Taek, Son, Il-Heon, Bae, Chul Min
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 30.08.2012; Elsevier
• Subjects: Aluminum base alloys; Applied sciences; Bolting; Bolts; Continuous hybrid process; Cross-disciplinary physics: materials science; rheology; Deformation; Exact sciences and technology; Fine-grained aluminum alloy; Forming; Fractures; Grain boundaries; Hardness; High-strength bolt; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Microhardness; Other heat and thermomechanical treatments; Physics; Production techniques; Rolling; Tensile tests; Transmission electron microscopy; Treatment of materials and its effects on microstructure and properties; Wire; Wire-drawing process; Continuous hybrid process; Fine-grained aluminum alloy; Transmission electron microscopy; High-strength bolt; Wire-drawing process; Deformation band; Drawing; High strain; Ultimate strength method; Material processing; Positron annihilation; Plastic deformation; Crystal defect; Grain boundary; Grain refinement; Rolling; Mechanical properties; Formability; ECAP; Microhardness; Tension test; Tensile strength; Thread; Manufacturing process; Fine grain structure; Ductile fracture
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2012.05.046

► Fine-grained AA6061-O was produced by a continuous hybrid process. ► It consists of rolling, ECAP, and drawing. ► High-strength bolt was manufactured with the fine-grained AA6061-O. ► The UTS and micro-hardness of the bolt was increased by 50%. ► The route C was better in making a uniform micro-hardness distribution in the bolt. It is well known that the development of a continuous manufacturing process to apply severe plastic deformation (SPD) is a major challenge for industrial usages to improve the mechanical properties of the material through grain refinement. In this study, fine-grained AA6061-O wire was manufactured by a two-pass hybrid process consisting of drawing, equal channel angular pressing and rolling in a continuous manner to investigate the effects of processing routes for two different routes, A and C, on the variation of ultimate tensile strength (UTS) and micro-hardness distribution. The UTS value (185MPa) of the specimen processed by the two-pass hybrid process with route A was higher than that of 171MPa obtained from the two-pass wire-drawing process and was equivalent to the level of 184MPa processed by the three-pass wire-drawing process. The average micro-hardness value (Hv 58.0) obtained from the two-pass hybrid process through route C was the highest among all the cases. According to transmission electron microscopy, the original grain was subdivided and elongated owing to deformation during the processes. The specimen processed by the two-pass hybrid process through route C showed smaller deformation bands and had potentially higher angle grain boundaries compared to the specimen processed by the two-pass wire-drawing process. Finally, the high-strength bolt was manufactured using the fine-grained AA6061-O wire prepared by the continuous hybrid process to check its formability. A ductile fracture at the first thread right above the jaw was observed in the bolt tension test of the manufactured bolt. The average micro-hardness value (Hv 56.1) obtained from the bolt manufactured with the specimen produced by the two-pass hybrid process through route C was higher than the one of Hv 50.5 obtained from the two-pass wire-drawing. It is demonstrated that the hybrid process might be useful in producing the grain-refined wire in a continuous process to manufacture high-strength bolts for practical applications.