【作者】 张铮；

【导师】 池成忠；

【作者基本信息】 太原理工大学 ， 材料学， 2007， 硕士

【摘要】 镁合金是最轻的一类金属结构材料，因镁的密排六方结构导致了镁合金的室温塑性低，成型能力差，限制了变形镁合金的工业应用。目前热处理细化晶粒成为提高镁合金塑性的一种有效手段，但是研究工作多集中在铸造态镁合金，关于挤压态镁合金型材的研究很少。挤压态镁合金型材应用日益广泛，同时要求型材的后续塑性加工能力越来越高。因挤压态镁合金型材有其独特的组织特点，故研究热处理工艺对其组织和性能的影响具有特别重要的意义。本论文以典型的挤压态AZ31管材作为实验材料，对其进行等温热处理实验和力学性能测试，为通过等温热处理方法提高管材的后续塑性加工能力奠定工艺理论基础和技术指导。对取自挤压成型的AZ31管材的试样分别按不同工艺进行等温热处理，实验主要影响因素包括加热速度(10℃／min、20℃／min、30℃／min、40℃／min)、保温温度(240℃、260℃、280℃、300℃、320℃、340℃)、保温时间(15min、30min、60min、90min、120min)和冷却方式(随炉冷、空冷、冷水、热水)；等温热处理结束后观察微观组织，测量晶粒尺寸和硬度变化，找到等温热处理时对晶粒细化效果影响显著的条件，确定晶粒最佳细化效果的热处理工艺；然后按照国家标准对管材进行力学性能测试。研究结果表明：挤压成型的AZ31镁合金管材组织中存在变形程度很大的孪晶、大尺寸晶粒、丧失了进一步变形能力的条带状组织等易导致后续塑性加工时变形不均，引起断裂的组织缺陷；采用最佳等温热处理工艺以20℃／min加热至300℃保温30min后空冷处理可以使试样平均晶粒直径从挤压态的50μm细化为19μm，同时基本消除上述组织缺陷；明显影响热处理效果的因素为保温温度、保温时间、冷却方式；室温下，采用最佳工艺热处理前后管材弧形试样的单向拉伸伸长率由10.8％提高至20.1％，管件的自由胀形极限伸长率由8.0％提高至14.9％。实验结果证明本论文得到的最佳等温热处理工艺可以明显改善挤压态镁合金管材的组织结构，有效提高管材塑性。更多还原

【Abstract】 Magnesium alloys is one of most lightweight structure materials, andhave found wide applications of aerospace, automobile and electronics due totheir high physical and mechanical properties. However, magnesium alloyshave poor formability and limited ductility at room temperature ascribed totheir hexagonal close-packed crystal structure. Grain refinement by heattreatment is an important measure to improve the mechanical properties ofmagnesium alloy. But now most reach findings are about as-cast magnesiumalloy, and there are few findings about as-extruded magnesium alloy, evenless about extruding sectional material.The extruding sectional material has unique texture, so its heat treatmentshould be different from other-materials. Now the wrought magnesium alloyis used more and more widespread, and consumers ask that the material hashigh quality, so it is important to research the heat treatment about extrudingsectional material. Therefor we take the AZ31 magnesium tube as the subjectinvestigated, have assays about heat treatment and mechanical property, andhope to get an example for the heat treatments of other extruding sectionalmaterials. Then we take the heat treatment about AZ31 tube by differenttechnologies. Elements include firing rate(10℃/min、20℃/min、30℃/min、40℃/min),holding temperature(240℃、260℃、280℃、300℃、320℃、340℃), holding time(15min、30min、60min、90min、120min),cool-downmethods (air cooling、furnace cooling、water cooling、hot water cooling),After heat treatment have an observation of microstructure, measure grainsize and hardness, find out significant elements, then get the best technology,at last take the mechanical property assay.It has been found that there are some texture flaws such as large grain、badly distorted twin and streaky structure. But recrystallization grains ofaround 19μm in diameter on average are obtainable through heat treatment at300℃for 30min by air-cooling, meanwhile the twin and streaky structurethat would weaken the plasticity of alloy are eliminated; significant elementsare holding temperature、holding time、cool-down methods. Mechanicalproperties of tube are obtained, simple tension elongation ratio of arc testsample increases from 10.8% to 20.1%, elongation ratio with elastic internaldie of tube increases from 8.0% to 14.9%.Test results show that proper heat treatment technology can optimizeas-extruded magnesium alloy and increases the plastic nature of AZ31 tube tomeet secondary operation.更多还原