AZ91D镁合金摩擦磨损行为及机理研究

【作者】 任峻；

【导师】 马颖；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2005， 硕士

【摘要】 AZ91D镁合金具有良好的铸造性能、力学性能,是应用最广的镁合金之一。但其凝固温度范围宽,很容易形成缩松缺陷,而且对其摩擦磨损性能方面的研究目前甚少,急需深入。而新型的触变成型技术兼有液态和固态成形的特点,能有效减少或消除缩松。所以,本文对触变成形AZ91D镁合金（简称ThF）的摩擦磨损行为进行了研究。 在Pin-on-Disc接触模式下的干磨损实验,研究了触变成形AZ91D镁合金以及经过固溶和时效热处理后的摩擦磨损行为,并与传统铸造AZ91D镁合金（简称CC）进行对比。根据摩擦系数的稳定性及耐磨性,探索出最佳的触变成形工艺参数,并结合磨面、磨屑形貌及成分分析,讨论了不同载荷下的磨损机理。结果表明,比较理想的触变成形参数为:坯料加热时间为60min、坯料加热温度为585℃和模具预热温度为300℃。随着载荷的增加,CC材料的磨损机制从氧化磨损、磨粒磨损为主逐渐转变为磨粒磨损、粘着磨损和熔融磨损,而ThF材料的磨损机制从氧化磨损为主逐渐转变为轻微剥层磨损、轻微粘着磨损和严重粘着磨损。即同样条件下,ThF材料的磨损程度比CC材料轻,触变成型有效地提高了材料的耐磨性。经固溶、时效处理后,都不同程度提高了材料摩擦系数的稳定性,固溶处理对材料磨损率影响较小,时效处理对磨损率影响较复杂。 同时,研究了触变成型AZ91D镁合金在往复滑动、Flat-on-Disc接触模式下的干摩擦磨损行为。结果表明:触变成型AZ91D镁合金的滑动磨损行为分为两大类,即轻微磨损和严重磨损,轻微磨损可以分为以氧化磨损、磨粒磨损为主的磨损和以磨粒磨损、轻微剥层磨损为主的磨损,严重磨损分为由严重塑性变形引起的磨损（严重剥层磨损）和熔融磨损。从磨损机制转变过程中所伴随的磨损率突变,判断出磨损机制转变发生时所对应的载荷和滑动速度,并以磨面形貌、磨屑形貌及成分以及磨面温度的的变化进一步证实磨损机制的转变。除熔融磨损外,每一种磨损机制所对应的磨面温度都与表达式(F^1/4V^1/2)存在函数关系。试验确定,轻微磨损到严重磨损的转变发生在摩擦面温度为75℃±5℃左右。基于上述特征绘制了触变成型AZ91D镁合金的磨损机制图。更多还原

【Abstract】 AZ91D alloy is one of the most commercial magnesium alloys because of its good foundry properties and mechanical properties. However, porosity can be easily formed in the castings due to its wide solidification range. The investigations on its wear behavior are very scarce, which needs to be intensively studied. The novel thixoforming technique can significantly reduce or eliminate porosity. Therefore, in this thesis, the wear characteristics of thixoformed （ThF） AZ91D alloy were investigated.The friction and wear characteristics of thixoformed AZ91D alloy were studied under dry friction pin-on-disk conditions, as well as those of the solid solution treated and aged AZ91D alloys. For contrast, the wear behavior of conventionally casting （CC） AZ91D alloy was also studied. According to the stability of friction coefficient and wear resistance, the optimal thixoforming parameters were confirmed. The wear mechanisms were also discussed by analyzing the morphologies of worn surfaces and wear debris, the changes in wear rate and friction coefficient. The results showed that optimal thixoforming parameters were: heating temperature of 585°C, heating time of 60min and mould preheating temperature of 300°C. The wear mechanism of CC alloy gradually changed in turn from oxidation and abrasive wear to abrasive wear, adhesive wear and melt wear with the increase of loading. But for the ThF alloy, the mechanism changed from oxidation wear to mild delamination wear, mild adhesive wear and severe adhesive wear. That is to say, the wear resistance of the ThF alloy is better than that of the CC alloy, and the thixoforming improved the wear resistance. The solid solution treatment and age treatment all improved the stability of average friction coefficient. The influence of solid solution treatment on wear rate was very small while the effect of aging was quite complicated.At the same time, the friction and wear behaviors of the ThF AZ91D alloy under dry friction reciprocating sliding motion were also studied. The results indicated that the sliding wear mechanism of the alloy included two kinds, mild wear and sever wear. The mild wear comprised oxidation and abrasive wear and abrasive and mild delamination wear while the severe wear included severe plastic deformation wear and melt wear. The loading and sliding velocity corresponding to the wear mechanism change were obtained from the values of loading and sliding velocity corresponding to a sharp change in wear rate. The wear mechanism change was further confirmed through analyzing the changes in wear surface morphology, wear debris morphology and its constituents and wear surface temperature. For each wear mechanism （except the melt wear）, the wear surface temperature obeyed a function with the expression of F^1/4V^1/2. The result showed that the wear mechanism changed from the mild wear to the severe wear at the surface temperature of 75°C±5°C. The wear mechanism map of the thixoformed AZ91D alloy was drawn according to the above analysis.更多还原