Precipitation behavior and quenching sensitivity of 2196 Al–Li alloy extrusion profile

Al–Li alloy usually has quenching sensitivity, affecting the mechanical properties of its forming components. This paper investigated the effects of extrusion parameter and quenching cooling rate on precipitation of quench-induced phases, aging phases and quenching sensitivity of extruded 2196 Al–Li alloy profiles. The results showed that a band structure constituted by coarse quench-induced phases including T1 (Al2CuLi) and fine aging phases including σ (Al5Cu6Mg2), θ' (Al2Cu) and T1 was formed as the quenching cooling rate was lower than that of air-quenched. With the increase of quenching cooling rate, the precipitation of quench-induced T1 phases was suppressed, and the size and density of other quench-induced phases, the width of precipitation free zone as well as the quenching sensitivity were significantly reduced. The grains of the profiles in extrusion and solution state both exhibited a fibrous structure, with a strong <112>//ED and <111>//ED orientation. The profile extruded at 370 °C × 1.5 mm/s exhibited abnormal coarse grains and gained a higher proportion of recrystallization after solution. The higher proportion of recrystallization and high angle grain boundaries would increase the hardness quenching sensitivity of 2196 Al–Li alloy. By comparison, extrusion parameters have a stronger impact on the strength quenching sensitivity than on the hardness quenching sensitivity. The effect of extrusion parameters on quenching sensitivity was less than that of quenching cooling rate. The elongation of the profiles increased with the decrease of quenching cooling rate at low extrusion temperature or speed, while it exhibited an opposite trend at high extrusion temperature or speed.