Effect of blooming methods on microstructure and properties of Al-Cu-Mg-Ag wheel hub forgings

This work provides two feasible processes for manufacturing large-scale Al-Cu-Mg-Ag alloy wheel hub forgings. Microstructure, mechanical properties, and corrosion resistance of the forgings prepared by extrusion-forging blooming or forging blooming are comprehensively evaluated and analyzed. The results reveal that compared with forging blooming, the yield and tensile strength at 25 °C of extrusion-forging blooming are almost equivalent. At high temperatures of 150 °C, 200 °C, and 250 °C, the yield strength shows little difference, while the tensile strength of extrusion-forging blooming is 2.4 %, 5.8 %, and 4.3 % higher, with lower elongations at all tested temperatures, respectively. Under the experimental conditions of Kt = 1 and R = 0.1, the 25 °C and 200 °C fatigue limits of extrusion-forging blooming are lower by 11.4 % and 5.0 % at the cycle of 10⁷, respectively. Both the intergranular corrosion and stress corrosion resistance of extrusion-forging blooming are superior to forging blooming. The reason is mainly correlated to the microstructure at the grain level, the deformation area fraction, and the mean grain size of the extrusion-forging blooming is 27.2 % and 43.9 % higher than forging blooming, respectively. The relatively coarse deformation structure mixed with fine grains may lead to load concentration in some areas, resulting in lower fatigue properties. On the other hand, the coarse grains reduce the diversity of corrosion paths compared to fine grains, reducing the tendency for large area flaking during corrosion, thus improving corrosion properties. The findings indicate that extrusion combined with forging blooming may sacrifice fatigue properties but improve corrosion resistance compared to simply forging blooming in Al-Cu-Mg-Ag wheel hub forgings manufacturing.