Microstructure And Mechanical Properties Of Solid State Recycling Of H62 Brass

Solid state recycling of materials,as a new concept of metal scraps recycling,is attracting more researchers' attention because of its low energy consumption and environmental friendliness.At present,various methods based on powder metallurgy and severe plastic deformation have been proposed to recycled metal scraps,and the recycled materials not only achieve the consolidation of metal scraps,but also often possess better mechanical properites than corresponding primary materials due to factors such as grain refinement and second phase strengthening.However,in the field of non-ferrous metal recycling,the traditional remelting method is still a primary way to recycle metal scraps.This method not only requires consumption of a large amount of energy,but also often lead to some negative impact to the environment.In this study,we propose solid state recycling of H62 brass wire by warm pressing,spark plasma sintering(SPS)and hot extrusion,and investigate the microstructure and mechanical properties of the recycled rods,By examining the transformation of the interwire boundaries and the tensile mechanical properties and fracture behavior of the recycled rods,the consolidation state of the original wires was studied.This research successfully verifies the feasibility of solid state recycling of H62 brass wires,and thus showing that solid state recycling by a combination of warm pressing/SPS and hot extrusion can be widely applied to recycling of non-ferrous metals.During the experiment,the compacts were prepared by the warm pressing and spark plasma sintering,then the H62 brass bars with different extrusion ratios were successfully prepared by hot extrusion of severe plastic deformation.The microstructure and mechanical properties of the recycled samples prepared under different process conditions were investigated separately.The microstructure of the phase distribution,phase content and grain size of the recycled samples were analyzed by Electron Back-Scattered Diffraction(EBSD),X-ray Diffraction(XRD),Scanning Electron Microscopy(SEM),and Optical Microscopy(OM).The results showed that the recycled samples were composed of phase of ? and ?'.The compact samples consisted of fine granular ?' phase and matrix a phase.The grain size of the warm pressing compaction was finest,which belonged to the ultrafine grain.The a phase grain in the hot extruded rod recrystallized relatively complete and distributed with equiaxed shape,while the ?' phase grain distributed along the extrusion direction with bamboo-like shapes.The mechanical properties of the recycled materials were analyzed by tensile test and hardness test.The results showed that the hardness of the warm pressing compaction is 162 HV because of its fine grain,which was higher than other samples.In terms of tensile properties,the yield strength and tensile strength of the recycled rods were 160 MPa and 400 MPa,respectively,exceeding basic requirements for casting H62 brass in soft state.But the plasticity was slightly poor and the elongation was less than 49%.Comparing the relationship between microstructure and properties,it was found that in the SPSed-hot extruded samples,the extrusion ratio is increased,so that the ?' grains of bamboo-like continuously distributed in the material along the extrusion direction are more elongated and their yield strength and tensile strength were improved correspondently.When analyzing the bonding state of the recycled material,it was found that the warm pressing and the SPS process fully realized the densification,so that the relative density of the compaction reached 98%or more.In the subsequent hot extrusion process,as the extrusion ratio increases,the relative density of the recycled rod increases slightly,but the overall change trend is not obvious.Further analysis of the transformation of the inter wire boundaries showed that the interwire boundaries in the warm pressed or SPSed compacts had polygonal shapes,so the bonding state of the material is poor.Subsequent hot extrusion of the compacts caused the interwire boundaries of the compact to be transformed into a linear shape,and these boundaries were discontinuously distributed along the extrusion direction.The plastic deformation of wires during hot extrusion caused the inter wire boundaries to be broken into fine particles which were distributed along logitdinal directions in the recycled rods.The interwire boundaries in the the extruded rods increase the strength of the material due to their hindrance to the dislocation slip needed by plastic deformation.In the meantime,the initiation and propagation of secondary cracks along the longitudinal direction during tensile testing show that there are locaitons along the interwire boundaries where strong metallgical bonding has not been estalished.On the other hand,the lack of wire separation and good mechanical properties of the tensile test specimens cut from the extruded rods shows a large fraction of the interwire boundaries have been transformed into grain boundries or interfaces with strong metallurgical bonds through rapid diffusion during the holding and diffusion process.This ensures the good performance of the recycled material.