文档介绍：摘要
本课题主要针对应用最广泛的AZ91镁合金进行研究,采用半固态重熔加热工艺和金相组织观察的方法,考察铸态树枝晶与挤压后的球形晶两种重熔加热后的组织的变化,探讨用于获得半固态组织的较佳的初始状态,并对两种状态的AZ91镁合金进行浸泡腐蚀试验,研究影响镁合金腐蚀速率的因素,为镁合金的半固态成型奠定基础。
研究结果表明:通过对金相组织分析得出,铸态的试样在560℃开始出现球状晶,挤压态试样就550℃就出现了球状晶。随保温时间延长或温度的升高,晶粒趋于圆整,由大到小,最后晶粒形态出现了异常,由原来独立球晶变为不规则的粗大球状晶;挤压变形对树枝晶转变成球状晶有促进作用;腐蚀试验结果表明:腐蚀速率随腐蚀时间延长逐渐减小,挤压态的试样耐蚀性低于铸态合金的试样。这主要与β相的含量、形态、和分布有关。当β相含量较少时,β相主要充当电偶的阴极;若β相分布不连续会加速α相的腐蚀过程。
关键字:AZ91镁合金半固态重熔加热耐腐蚀性
ABSTRACT
The main subject of the study for the most widely used AZ91 magnesium alloy,with Semi-solid remelting heating process and microstructure observation,inspected changes in anizations investigated cast dendrites and squeeze both spherical crystal remelting heated and explored better initial state for semi-solid magnesium alloy of two states for immersion corrosion was tested,studying factors affecting the corrosion rate of magnesium alloys,which laid the foundation for the semi-solid forming of magnesium alloy.
The results showed that, spherical crystal was found in the cast of the specimen at 560 ℃ while extruded samples at 550 ℃ by analysis of the the holding time or temperature increases, the grain tended rounded, descending,and the last grain morphology appeared abnormal, irregular coarse spherical crystal from the original independent Spherulite ;anization from dendrite into spherical crystal was promoted pressional corrosion test results showed that: the corrosion rate gradually decreased with the etching time extending, while the specimen corrosion resistance of squeezed state was lower than the cast alloy mainly depended on the content of the β phase, morphology and β phase content was small, the β phase mainly acted as a galvanic cathode;The β phase discontinuous distribution would accelerate the corrosion process of the α-phase.
Key words: AZ91Magnesium alloy semi-solid remelting heating corrosion resistance
目录
第一章绪论 1
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