Composition-Optimized Cu-Zn-(Mn, Fe, Si) Alloy and Its Microstructural Evolution with Thermomechanical Treatments

High strength and large ductility of existing Mn-containing brass alloys need to be further improved when used as slippers of friction-pair materials, which could be achieved by tuning alloy composition and thermomechanical treatments appropriately. The present work optimized the amount of minor-alloying elements M (M = Mn, Fe, Si) in Cu-Zn alloy via a cluster formula approach and then investigated the microstructural evolution of the designed alloy with different thermomechanical treatments. As-cast alloy ingots were solid-solutioned at 1093 K (820 °C) for 3 h, hot-rolled at 923 ~ 1023 K (650 ~ 750 °C), and then aged at 673 ~ 723 K (400 ~ 450 °C) for 1 ~ 2 h, respectively. It is found that the alloy matrix consists of the main FCC-α phase plus a small amount of BCC-β and M5Si3 phases, among which the M5Si3 exhibits three types of primary, fine, and nano-scaled particles. The mechanical property varies with the thermomechanical treatments due to diverse microstructures (especially the morphology of M5Si3 particles), in which the high strength (σUTS > 580 MPa) and large ductility (δ = 16.3 ~ 29.4%) could be achieved simultaneously in 673 K (400 °C). The optimal matching of high strength and large ductility makes the current alloy more suitable as an alternative slipper material. The strengthening effect was further discussed in light of various strengthening mechanisms, and the calculated strength increment is well consistent with the experimentally measured yield strength.