Continuous high strength aluminum bolt manufacturing by the spring-loaded ECAP system

Aluminum alloy 6061-T6 was used to produce an ultrafine-grained specimen by spring-loaded equal channel angular pressing (ECAP), which was continuously applied to a commercial multi-stage former at a production rate of 30 rpm at room temperature to manufacture high strength aluminum bolts. In order to increase the mechanical strength of the manufactured bolt, the bolt-forming process was introduced based on extrusion process in the present work. With the specimens processed by a single pass ECAP, underfilling at the bolt head and surface cracking at the flange of the produced bolts were observed due to the geometry of the ECAPed specimen and friction at the die interface, respectively. To remove these defects, modified route C for the second pass ECAP and aluminum fluoride coating with metal soap for the initial specimen were applied. Finally, the ultrafine-grained aluminum bolts were successfully manufactured in a continuous sequence. Both the ultimate tensile strength (UTS) and elongation to fracture of the manufactured bolts increased compared to the conventionally made bolts. According to the present investigation, an innovative approach utilizing the ECAP to develop high strength bolts without modifying conventional material is demonstrated.

► A ultrafine-grained aluminum bolt was made by a continuous spring-loaded ECAP system.
► Flange cracking and underfilling were observed in the bolt based on first pass ECAP.
► They were removed by introducing surface coating and a modified route C of 2nd pass.
► The UTS and elongation of the UFG bolt increased compared to the conventional one.