Heat Treatment Process And Corrosion Resistance Of Wire Arc Additive Manufacture ZL114A Alloy

ZL114A alloy is an Al-Si-Mg ternary alloy.It is widely used in transportation,navigation,aviation and other fields.In traditional manufacturing and processing,there are some problems such as long production cycle,difficult processing and high manufacturing capital cost for thin-walled parts,high hardness parts,large complex parts and some high-performance parts.Wire arc additive manufacturing（WAAM）technology can effectively avoid these problems and realize rapid,low-cost and high-efficiency manufacturing of products.At present,for the aluminum alloy product made by additive manufacturing,post heat treatment systems such as single-stage solution aging,double-stage solution aging,direct aging and regression reaging can be adopted to improve the comprehensive performance.In this paper,ZL114A alloy made of wire arc additive manufacture was studied.The effects of heat treatment systems such as solid solution time,aging temperature,aging time and regression reaging on the microstructure,hardness and corrosion resistance of product were studied.The metallographic structure of the alloy was observed by optical microscope;The corrosion resistance of the alloy was tested according to Tafel polarization curve and electrochemical impedance spectroscopy;The change of alloy phase composition during heat treatment was determined by scanning electron microscope and energy dispersive spectrometer;The phase composition and crystal plane structure of the alloy were determined by X-ray diffraction;The Vickers hardness value of the alloy is determined by hardness tester;The composition of the passive film formed by the alloy was determined by X-ray photoelectron spectroscopy;Finally,the corrosion process and morphology of the alloy were observed by immersion method,and the corrosion mechanism of the alloy was discussed.The experimental results show that when the solid solution temperature is 540℃,the fine grain structure of the deposited alloy gradually disappears and the hardness of the alloy first decreases and then increases with the increase of solid solution time.The polarization curve,pitting potential and corrosion resistance of the alloy were significantly improved.Under540℃/10h solid solution process,when the aging temperature is 175℃,the aging time is 4h～6h,the precipitation of aging precipitates is less,and the hardness of the alloy is low;Within6h～12h,the aging precipitates of the alloy increased significantly,and the hardness value of the alloy increased significantly;The peak aging is reached at 12h,but the corrosion resistance of the alloy is greatly reduced.In order to improve the corrosion performance of the alloy after heat treatment at 540℃/10h+175℃/12h,the heat treatment process of 540℃/14h+175℃/12h+260℃/30min+175℃/12h regression reaging was carried out.Compared with the aging solution treated aluminum alloy,after immersion test,the number of pitting pits,the depth and width of pitting pits are reduced,and the corrosion resistance of the alloy is improved,but the hardness is slightly reduced;For the alloy made of wire arc additive manufacture,the corrosion type of as-deposited alloy is total corrosion;After solution aging treatment,the local corrosion of the alloy is mainly pitting corrosion.The passive film produced by ZL114A alloy made of wire arc additive manufacture is mainly composed of Al₂O₃,Al OOH,Si₂O₃,Si O₂ and other substances.The corrosion morphology of the as-deposited sample is the dense Al₂O₃ corrosion product attached to matrix,which is square fine particles;After solution aging heat treatment,obvious passive film and spherical silicon oxide corrosion products can be seen on the surface of the sample;The corrosion products on the surface of the sample after regression reaging treatment are mainly protruding spherical alumina and silicate.The three states of alloy passivation contain a small amount of Sr element,and there is a small amount of Mg element in the alloy passivation film after deposition and solid solution aging treatment.