【作者】 刘敬福；

【导师】 李荣德；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2008， 博士

【摘要】 喷射成形将金属熔体雾化和雾化液滴沉积合为一体,可直接由液态金属制备具有快速凝固组织特征的大块金属坯体。本文在ZA35合金进行Mn合金化基础上,采用喷射成形技术制备高锰ZA35合金,对其制备过程和致密化工艺、力学、耐磨和耐蚀性能进行研究,以期改善ZA合金的显微组织、消除低熔点共晶、提高合金元素固溶度等,使合金性能得以大幅度提高,拓宽其应用范围。通过实验,本研究取得主要成果如下:通过选用适当的工艺参数,利用喷射成形技术制备出高锰ZA35合金。与铸态组织相比,喷射成形合金为细小均匀的等轴晶,尺寸约为30μm,富Mn相消失,Mn全部固溶于基体。优化的热挤压工艺参数为挤压温度260℃、挤压比12、比压430MPa。热处理工艺对喷射成形高锰ZA35合金各项力学性能影响明显。时效过程中,新相析出使位错运动受阻和多种富锰相的弥散强化使合金硬度随时间的延长出现双峰现象。热力学稳定相MnAl₆优先从过饱和的α-Al（η-Zn）中析出,随时效温度升高和时效时间延长,亚稳相Al₁₁Cu₅Mn₃和CuMnZn依次析出。在挤压和热处理后合金中均出现纳米级晶须状和颗粒状MnA₆。随着温度提高,合金断裂机制由脆性断裂逐渐转变为韧性断裂。喷射成形高锰ZA35合金的强化机制主要有固溶强化、细晶强化、第二相强化和位错强化。在实验速度和载荷下,喷射成形高锰ZA35合金的摩擦因数和磨损率均比铸态合金低,具有更高的耐磨性和减磨性。喷射成形合金的磨损机制主要是磨粒磨损和疲劳磨损,而铸态合金的磨损机制主要是磨粒磨损、粘着磨损和部分氧化磨损。喷射成形态高锰ZA35合金盐雾腐蚀动力学曲线的抛物线速率常数小,腐蚀程度轻微。合金在盐雾下腐蚀原因是富锌η相的优先溶解,喷射成形态合金锰全部固溶,降低η相和α相电位差,腐蚀驱动力降低,减缓腐蚀。在中性沸腾水介质中,喷射成形态合金中负电性的α富铝相作为阳极溶解时,腐蚀产物容易阻挡作为短路扩散的细小晶界,阻止侵蚀性介质扩散,减缓腐蚀。固溶时效处理使合金组织向平衡组织转变,降低晶界活性,减小电化学腐蚀倾向。更多还原

【Abstract】 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.更多还原