Fatigue Properties of AA6061 and AA7075 Extruded Rod after Retrogression Heat Treatment and Thermo-Mechanical Treatment

摘要

In the past. Retrogression Heat Treatment (RHT) was mainly used for difficult bending and forming operations conducted on 6xxx aluminium alloy extrusions without fracture or deterioration of properties in the formed material. Typically, RHT as described in this and previous studies involves the rapid localized heating of precipitation hardening alloys in order to temporarily re-solutionize the hardening precipitates that form upon earlier natural or artificial aging. Unlike conventional heat treatments, where the cycle involves heating to maximum temperature, holding at this temperature for some period of time, and quenching, the RHT process takes place in seconds, with quenching right after the temperature peak. Although it is widely known that precipitation harden-able 6000-and 7000-series alloys such as 6061 and 7075 are best formed in the as-quenched or annealed condition, it is observed that after RHT, even 6061-T6 and 7075-T6 materials can be easily formed. Since the introduction of the RHT process, numerous developments have evolved and applications have spread worldwide within various industries.