Characterization of microstructure and local mechanical properties of friction rolling additive manufactured Al[sbnd]Li alloy under repeated thermal–mechanical cycles

Abstract

Deformation-based friction rolling additive manufacturing (FRAM) is a promising solid-state additive manufacturing (AM) approach for producing non-fusible, weldable AlLi alloys. Along with the thermal cycles of conventional AM methods, the materials deposited during FRAM are affected by the repeated force of a tool head. However, the effect of repeated thermal–mechanical cycles on the microstructure and mechanical properties of a deposited material remains unclear. This study attempts to develop mechanisms by characterizing the microstructure and local mechanical properties of FRAM-ed AlLi alloys, with different deposition heights and those that underwent a different number of thermal–mechanical cycles. A recrystallized microstructure is successfully obtained and fine equiaxed grains are observed in the deposited material without pores and cracks. The value of ultimate tensile strength (UTS) reaches 98–91% of the base metal from the top to bottom regions. Under repeated thermal–mechanical cycles (from the top to bottom region), the grain size increases from 2.0 μm to 6.5 μm. The texture strength and diameter of δ’ precipitate also increase, while the volume fraction decreases. Together, they lead to a decrease in local UTS and elongation, from 450.7 MPa to 415.1 MPa and from 10.4% to 6.3%, respectively. The relationship between thermal–mechanical cycles and microstructure established in this study provides the foundation for subsequent research on FRAM thermal balance and microstructure regulation.