Preaparation And Properties Research Of Aluminum Brass By Powder Metallurgy

The temperature during the casting process is relatively high when casting aluminum brass,it will require long time to cool to room temperature,which the grains are easily growing and form complicated inter metallic compounds to reduce the mechanical properties of material.In this study,powder metallurgy was used to mix pure aluminum powders with water atomized Cu40Zn brass powders before sintering them at a suitable temperature.Through interface reaction between copper and aluminum,aluminum-copper-zinc ternary metastable ?-phase was formed at a lower temperature,annealing metastable ?-phase at suitable temperature,internal atoms dissolving and forming solid solutions with different components.The solid solutions with different components will precipitate again during the cooling,which solid solutions with lower zinc will form a phase.In the solid phase reaction process,the high temperature range in the casting process is avoided.The new phase nucleation and growth process can be effectively controlled with avoiding the growth of grains and the formation of high temperature brittle phases,thereby effectively improving the material properties.The experimental results show that aluminum brass prepared by powder metallurgy has a significant grain refinement and strengthening effect.During the solid phase sintering reaction,the addition of lower amount(below 1.5 wt.%)of aluminum to the Cu40Zn powders will reduce the a phase and increase the ? phase with increasing strength.When the aluminum content reaches 2 wt.%,the a phase was completely eliminated in the substrate,and the overall structure of the aluminum brass becomes a single ? phase after the interface reaction between the aluminum element and the copper.The metastable single-phase only exists in certain composition and temperature.The temperature of holding time and cooling rate also affect the content of precipitated phase.When the content of aluminum is added to 4%,all of grains are coarsen,and the two phases that a and ? of the original powder were transformed into ? and ?,and the material suffered brittle fracture rather than toughness fracture.So the phase composition and performance can be adjusted by controlling the content of aluminum and Cu40Zn.With a systematic study of aluminum brass system that the aluminum content of 2 wt.%,we found when the aluminum content is reached 2 wt.%,the grain refinement is mainly caused by the solid solution-dissolvation and interfacial reaction of the aluminum element in the brass.During the rising temperature process,the aluminum element through the interface reaction with the brass matrix,forming Al2Cu3 and other metastable phases will consume the copper element continuously,so that the relative content of zinc element in a certain area of the brass matrix is increasing.After the ?-phase disappeared completely,there is still a difference in composition between the surface and the inside of the primary particles.As the diffusion reaction continues,the metastable copper-aluminum intermetallic compound formed at the interface but dissolving and decomposing later.Segregation occurs in the localarea where the composition of this area is changed.Due to the composition of each area is different,?-phase nucleation will occur in areas with high copper content and low zinc-aluminum content during the cooling process.The ?-phase weather growing up depends on the cooling rate and the state of the diffusion reaction during the holding time.Transmission electron microscopy analysis of the Cu40Zn-2 wt.%Al extruded aluminum brass sample shows that the hot extrusion process of aluminum brass will uniformly form a large number of dislocations and lattice distortions inside the material,which is good for the segregation of dissolved atoms.This conditions enable the atom segregation regions to be finely and evenly distributed inside the matrix,increasing the nucleation rate of the ? precipitated phase during the cooling process.After nucleation of the new phase,it is difficult to get the copper elements required form out of the segregated area to grow,and the overall structure is refined,and the precipitated ? phase can be dispersed in the matrix..In this paper,using powder metallurgy to mix aluminum powder with brass powder,studying the solution-desolvation reaction process by solid-phase reaction sintering,including interface diffusing reaction and the formation process of metastable phase,it is found that the brass matrix undergoes a transition from ? phase to a single metastable state ? phase.The metastable state ? phase will take place atoms gathering by spinodal decomposing in some area,which contain more Cu atoms will precipitate ? phase.After hot extrusion,the grain will be refined again,and the final mechanical properties will be greatly improved and maintain good corrosion resistance.