Influence Of Ce On Microstructures And Properties Of High-strength Wear-resistant Manganese Brass

The HMn64-8-5-1.5 brass is a high-strength wear-resistant brass belonging to Cu-Zn-Mn series complex brass, a common synchronizer gear ring material. With the rapid development of automotive industry, a higher requirement of property of such material is put forward, especially for tribological properties. In order to improve the tribological properties of the manganese brass, add different content of rare earth Ce into HMn64-8-5-1.5 brass, then tested strength, hardness and tribological properties. The microstructures of brasses with different content of Ce were studied by using optical microscopy, XRD, SEM and energy spectrum analysis. The wear mode and mechanism was studied by using SEM to analysis of the wear surface and subsurface. The following conclusions are drawn from this work:There is ?-phase matrix, huge [Mn(Fe)]5Si3 hard phases, tiny Mn5Si3 hard phases and Pb-phases in the microstructures of HMn64-8-5-1.5 brass with different content of Ce. The addition of rare earth Ce into brass can refine the matrix grain. With the Ce addition content increasing to 0.25 wt.%, the size of ?-phase matrix decreased from 155?m to 60?m in as-cast alloy, and 60?m to 35?m in extruded brass. Meanwhile, the Ce addition contributes to the extraction of tiny hard phases and can improve the distribution of hard phases.There is little difference in hardness of HMn64-8-5-1.5 brasses with different content of Ce. The brinell hardness range from 225 HB to 235 HB in as-cast and extruded alloys.The fracture mode of HMn64-8-5-1.5 brass is microvoid accumulation fracture caused by the second phases breaking up and developing into dimples. The addition of Ce can refine matrix grain, inhibit the crack extension and improve mechanical properties. But it also can lead to precipitation of tiny hard phase out of grain boundaries, and thus increase the quantity of crack origins in the process of stretching and deteriorate mechanical properties.Two opposite factors affected the mechanical properties of brass together, so the strength increased and then declined with the increasing of Ce. The tensile strength is about776 MPa and yield strength is 614 MPa when there is 0.25 wt.% Ce in the brass.The addition of Ce into HMn64-8-5-1.5 brass can improve tribological properties. The wear-resisting property of as-cast brass contains 0.15 wt.% Ce increased about 20%compare with the simples without Ce. The extruded alloy containing 0.25 wt.% Ce have better tribological properties. The wear-resisting property increased about 19% in dry friction, and 32% in wet friction.According to the analysis of wear surface and subsurface after dry friction, the wearing mode between manganese brass and GCr15 steel in dry friction with 200 N load is fatigue delaminate wearing accompanied with adhesive wearing and abrasive wearing, while the wearing mechanism is exhausted level attrition. With the increasing load, the wear rate increased sharply and the wearing mode turned mainly on adhesive wear. In the dry friction with GCr15 steel, the load should not be exceed 400 N.