【作者】 胡小石；

【导师】 吴昆；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2007， 博士

【摘要】 本文以研制和开发高阻尼镁合金为目的,设计和制备了具有不同固溶度合金元素的纯镁、Mg-Al系、Mg-Ni系和Mg-Si系合金。利用光学显微镜(OM)和透射电子显微镜(TEM)等方法观察合金的微观组织特征;通过拉伸试验和硬度测试评价合金的力学性能;通过机械动态分析仪(DMA)研究合金的低频阻尼性能随应变和温度的变化规律;通过热处理、热挤压变形和室温小变形量拉伸等手段研究合金阻尼性能的稳定性;通过正电子湮没等测试手段分析影响镁合金阻尼性能的点缺陷种类。揭示了镁合金低频阻尼行为的变化规律及其影响因素,为开发高阻尼、高性能镁基材料奠定了良好的基础。对铸态纯镁和镁合金阻尼性能的研究表明:纯镁和镁合金的阻尼机制属于位错型。镁合金的阻尼性能强烈地受到合金元素的种类和数量的影响;向纯镁中加入固溶度较高的Al元素,会极大降低镁合金与应变无关的阻尼值,但Al原子的加入可以改变铸态纯镁中点缺陷的分布形式,因此在大应变振幅下含Al量较少的镁合金(<1%)阻尼值大大超过纯镁的阻尼值。向纯镁中加入固溶度极低的Ni和Si元素,在合金中的初晶α-Mg相具有一定尺寸和体积比例的情况下,Mg-Ni和Mg-Si合金具有较高的阻尼性能;在小应变振幅下,由于初晶α-Mg相中具有高于纯镁的位错密度,这类合金的阻尼值高于纯镁的阻尼值。铸态纯镁、Mg-Ni和Mg-Si合金在室温附近的高阻尼值来源于80oC附近的阻尼峰P1,该峰是由初晶α-Mg相中的位错与晶格中的点缺陷交互作用引起的。在230oC附近的P2峰为晶界阻尼峰。当加入的Al元素含量超过1%时,阻尼-温度谱中的P1和P2阻尼峰被抑制。热处理对具有一定尺寸初晶α-Mg相的合金的阻尼性能有显著的影响,这种影响归因于初晶α-Mg相中非平衡状态的点缺陷受热处理的影响发生扩散,并重新分布造成的。铸态镁合金中的溶质原子以非平衡溶质原子团的状态存在于初晶α-Mg相中,钉扎在位错上的钉扎点较少;当热处理温度较低时,溶质原子沿位错扩散,使位错上的弱钉扎点数量明显增加,晶格中的点缺陷数量降低。对于超过350oC的高温热处理,点缺陷的扩散速度明显加快,溶质原子团快速分解,并且很快达到平衡状态,很多溶质原子扩散至晶界处,部分原子均匀分布在晶格中。虽然这类镁合金中杂质点缺陷数量并不多,但它们受热处理的影响发生重新分布后,对合金的阻尼性能和P1、P2阻尼峰有相当显著的影响。与上述镁合金相比,热处理对Mg-Al合金阻尼性能的影响非常小,这是由于Al含量较高,使位错上的弱钉扎点之间的长度LC降低到一定程度后,合金与应变振幅无关的阻尼值基本达到最小值,虽然热处理可以显著地改变合金的微观组织,但无法大幅度地改变固溶态Al原子的数量,因此该类合金的阻尼性能不会明显地受到热处理的影响;变形使Mg-1%Al和Mg-1%Si合金的室温阻尼值下降,并且相比之下,具有高阻尼性能的Mg-1%Si合金的阻尼值受变形的影响更大,3%以上的室温拉伸变形量即可抑制P1阻尼峰的出现,后续退火不能使由于挤压变形而消失的P1阻尼峰得到恢复。变形使Mg-1%Al和Mg-1%Si合金在高温测试范围内获得显著高于铸态合金的阻尼值,但这种高阻尼值是不稳定的,它与变形后的合金在高温范围内的回复再结晶有关,再结晶过程中位错和晶界的运动使合金得到高阻尼值,一旦再结晶过程结束,阻尼值就恢复到铸态合金的阻尼水平。更多还原

【Abstract】 On the purpose to research and develop high damping Mg alloys, we designed and fabricated pure Mg, Mg-Al alloys, Mg-Ni alloys and Mg-Si alloys which containing elements which possess different solubilities in Mg. The microstructures characteristics of these Mg alloys were observed by OM and TEM. The mechanical properties were tested by tensile test and hardness test. The strain dependent and temperature dependent low frequency damping capacities of these alloys were studied by DMA. We studied the stabilities of the damping capacities in these Mg alloys by heat treatment, hot extrusion and small tensile deformation at room temperature. The point defects types which influence the damping capacities of Mg alloys were analyized by positron annihilation method. This paper revealed the low frequency damping behaviors of Mg alloys and their influence factors, established a good foundation to develop high damping Mg based materials with high performances.The research results shown that, the damping mechanism of pure Mg and Mg alloys is dislocation damping. The damping capacities of Mg alloys were strongly influenced by the type and amount of alloying elements. When Al which has high solubility was added into Mg, the damping capacity will heavily decrease. But small amount of Al atoms (<1%) could changed the distribution condition of foreign atoms in Mg and predominantly increased the damping value at high strain level. When Ni or Si which has very low solubility was added in Mg, and there are still largeα-Mg phase in these alloys, the damping capacities of these alloys remain high value, especially at small strain level. There are damping peaks P1 and P2 in pure Mg, Mg-Ni and Mg-Si alloys, which located at 80oC and 230oC, respectively. P1 is considered to be induced by the interaction between dislocations and the point defects in the crystal lattice of Mg, and P2 is the grain boundaries damping peak which is caused by the grain boundaries sliding at high temperature.Heat treatment has remarkable influence on the damping capacities in Mg which possessα-Mg phase with certain size. This is caused by the diffusion and redistribution of the nonequilibrium point defects groups inα-Mg phase by heat treatment. The point defects of as-cast Mg are existed as nonequilibrium point defects groups inα-Mg phase, and the amount of weak pinning points on dislocations are very small; when the heat treatment temperature is relatively low, the point defects diffussed along dislocations, and this made the amount of weak pinning points on dislocations increased, and the amount of them in the crystal lattice decreased; when the heat treatment temperature is higher than 350oC, the diffusion rate of point defects is strongly increased, and the point defects groups decomposed rapidly and reach balance very fast. Some of the point defects are located in the grain boundaries, and parts of them are evenly distributed in the crystal lattice. Though the amount of these point defects is not large, they have strong influence on the damping capacities and P1 and P2 damping peaks in Mg alloys when the distribution condition of them is changed. Compared with Mg alloys withα-Mg phase, the influence of heat treatment on damping capacities of Mg-Al alloys is very small. This is because that the Al content is high enough, which made the length LC between weak pinning points on dislocations decreased to a certain value, therefore the Mg-Al alloys got the saturated damping values. Though heat treatment could remarkably changed the microstructures of these Mg-Al alloys, it will not strongly change the content of Al in it, and then, the damping capacities of these alloys will not strongly influenced by heat treatment.The room temperature damping capacities of Mg-1%Al and Mg-1%Si alloys were decreased after deformation, and the influence of deformation on the damping capacity of Mg-1%Si alloys is more remarkable than that of Mg-1%Al. When the room temperature tensile deformation is higher than 3%, the P1 peak will be inhibited; subsequent annealing will not recover the inhibitition of P1 peak which was caused by extrusion. Mg-1%Al and Mg-1%Si alloys could abtain high damping values at high temperature range after deformation, but these high damping values are not stable. The high damping values at high temperature region is related to the movement of dislocations and grain boundaries during recovery recrystalization. The damping capacity could reback to the damping level of as-cast alloys when the recrystalization process is finished.更多还原