Study On The Effect Of ECAP Process On The Second Phase And Performance Of H65 Brass

According to the overseas and domestic research status that researches on the evolution of second phase exsistence (structure, quantity, shape, size, distribution) and its effects on alloy properties under conditions of severe plastic deformation were not sufficient and systematic, This thesis adopted the way of ECAP which can not only realize large deformation but also effectively refine grain to carry out ECAP deformation experiment and ECAP-Rolled experiment on H65 brass alloy. The deformation rule of ECAP and evolution of microstructure were analyzed, and the effects of second phase existence on alloy properties were explored by analyzing the variation of mechanical and physical properties. The conclusions can be drawn as follow:(1) Analysis of ECAP deformation rule of H65brass alloyIt was found that friction had a great effect on extrusion force, and the extrusion force decreased with the increase of inner angle and external angle of die, especially, the influence of inner angle on extrusion force was bigger than that of external angle. The variation of extrusion load in process of ECAP can be divided into four stages:gradual increase, rapid increase, stable fluctuation within certain limits and gradual decrease. The maximum equivalent strain distribution concentrated within 3 to 9 mm in the center of samples,and even passes can obtained more uniform deformation. The samples that in corner of inner angle was the prior place to crack. The flow velocity was basically stable except at the corner of die route where the flow velocity varied.(2) Effects of ECAP and rolling process on alloy propertiesBoth the hardness and tensile strength of H65 brass basically showed a trend to increase rapidly at first, then increase slowly and decrease slightly in the end. The maximum hardness of 239.3 HV and maximum tensile strength of 632.20 MPa were obtained in third extrusion pass of ECAP, which were improved by 238% and 122.21% compared with that of as-cast samples. After rolling, the hardness and tensile strength of samples was improved greatly in ECAP process at the same pass, and obtain the maximum 244.6 HV and 781.25 MPa respectively. Conductivity slightly decreased with the increase of ECAP passes; Rolling can improve the inhomogeneity of hardness and plasticity.(3) Effects of second phase evolution on alloy propertiesβ phase in as cast state mainly presents as semi-continuous mesh or non-directional short rod. In odd passes of ECAP, β phase was stretched into long strip, and the angle between deformed β phase and extrusion direction was between positive 30 and 40 degrees, and β phase space became closer; In even passes of ECAP, β phase was deformed into short rod, and the angle between deformed β phase and extrusion direction was between positive 40 and negative 40 degrees, and β phase space became sparse. After rolling experiment, almost all the β phase became longer with decreasing phase space, and the angle was between 0 and positive 10 degrees.The hardness improvement of brass alloy by β phase was mainly in the first extrusion. The tensile strength which decreased with the increase of angle between the P phase and tensile axis and β phase space.