Achieving an ultra-high strength in a low alloyed Al alloy via a special structural design

Abstract

An ultrafine-grained (UFGed) low alloyed aluminum alloy (6061 Al alloy) with a special nano-sized spherical precipitate structure was achieved by friction stir processing (FSP) and post-FSP aging. The evolution of the grains and precipitates during post-FSP aging and their contribution to mechanical properties were investigated. Under a low rotation rate (200 rpm) with water cooling, the average grain size of the FSP sample was only 200 nm. The ultimate tensile strength of the UFG 6061Al alloy aged at 100 °C for 20 min achieved 573 MP with a high elongation of 17%. This strength was nearly 90% higher than that of 6061 Al-T6 alloy (∼300 MPa), and was equivalent to that of commercial 7075Al-T651 alloy (∼572 MPa, the typical high alloyed Al alloy). Such a good mechanical property was attributed to the good thermal stability and the accelerated precipitation of the FSP UFGed structure under the low-temperature and short-time aging conditions. Further, the contribution of various strengthening mechanisms to the total strength in post-FSP aged Al alloys was quantitatively evaluated. This work provides an effective strategy for obtaining low alloyed high-strength Al alloys, which is beneficial for reducing environmental burdens and improving long-term sustainability.