Fabrication And Properties Of Spray Forming High Mn ZA35 Alloy

During spray forming,a liquid metal stream is atomized into a spray of droplets by high-pressure gas jets and subsequently these atomized droplets are deposited and solidified on a substrate.By optimization of the processing parameters,near net shape products may be produced with refined microstructure,extended solubility of alloying elements and rare microsegregation.The mechanical property,wear and corrosion resistance properties of ZA35 alloys prepared by spray forming technology with high alloying element Mn were investigated.The purpose of this research is to improve the microstructure and properties of ZA alloy,and to extend its application field.The main results are summarized as follows:The ZA35 alloy with 3.5%Mn is manufactured with spray forming technique using the optimized process parameters.It is indicated that the microstructure of spray formed high Mn ZA35 alloy is composed of equaxial grains with the size of 30μm.The element Mn exists mainly in the form of independently Mn-enriched hard phase or near the interfaces of grains of casting ZA35 alloy,on contrary,the independently Mn-enriched hard phases are not found in spray formed high Mn ZA35 alloy.The solid solubility of Mn in ZA35 matrix is shifted considerably to a higher level by spray forming.The proper parameters of heat squeezing are:temperature is 260℃,squeeze ratio is 12 and the specific pressure is 430MPa.Heat treatment process has a significant effect on mechanical properties of spray forming ZA35 alloy with high Mn account.With the precipitation of new phases,the dislocation-moving is restricted,and the second phase strengthening also contributes to the hardening.So the aging curves demonstrate the phenomenon of double peak.The stable phase of MnAl₆ is preferentially precipitated from the supersaturatedα-Al(η-Zn).With the increase of aging time and temperature,the metastable phases of manganese(Al₁₁Cu₅Mn₃ and CuMnZn) are precipitated.The nano whisker and particle of MnAl₆ are obtained in spray formed high Mn ZA35 alloy after heat squeezing and heat treatment.With the increase of temperature,the fracture mechanism of spray forming alloy shows toughness fracture.In addition to fine grain strengthening,second phase strengthening,solid solution strengthening and dislocation strengthening are the main strength mechanism of spray forming alloy.Under the working parameters of sliding speed and load,the friction coefficient and wear rate of spray forming alloy is lower than that of casting alloy.Spray forming alloy has higher wear resistance,as well as good anti-attrition than those of the cast alloys with the similar composition.The main wear mechanism of the spray forming alloy is in the form of grain-abrasion and fatigue wear,and for the cast alloy is in the form of grain-abrasion, sticking wear and oxidizing wear.Salt spray corrosion behavior of spray forming ZA35 with 3.5%Mn alloy was studied. The result shows that the curve of corrosion dynamic is parabola,the corrosion ratio is less than that of cast alloy.The corrosion reason is the dissolution ofηphase.The solid solubility of Mn in ZA35 matrix is considerably shifted to a higher level by spray forming, so the potential difference betweenηphase andαphase is lowered.Therefore,the corrosion rate can be limited.In the media of boil water,as anode polar the Mn-enriched Al phase in spray forming alloy dissolves.The good anti-corrosion performance of alloy could be mainly attributed to the barrier effect of corroded product against the diffusion of corrosive media.The corrosion trend can be restrained by the treatment of solid solution and aging.