材料期刊网

测量了Mn-Cu-Al三元合金(含56-60wt-％Mn,0-3.59wt-％Al)在-150—150℃的声频内耗,发现当试样在调幅线的温度范围内进行时效时,内耗随着时效时间的增加而增加,并在特定的时间内达到极大值.时效温度越高,达到极大值的时间越短.在时效一定的时间后出现马氏体相变峰和孪晶界面弛豫峰.相变峰随着时效时间的增加而向高温移动;弛豫峰则出现在15℃左右(频率约1kHz),测得其激活能是0.56eV. 在调幅线内时效使合金的硬度、强度及脆性墙加,Al元素有增加合金的强度而降低其内耗的作用.实验结果表明,在450℃时效2—3h,可得到合金的内耗和强度的最佳综合指标. 根据内耗、模量、金相检验和X射线分析的结果,认为调幅分解后产生的富Mn区是合金发生相变和高内耗的来源,也是合金的强度增加和韧性降低的原因.

Internal friction and elastic modulus of ternary Mn-Cu-Al alloys con-taining 56--60 wt-% Mn, 0--3.59wt-% Al were measured with acoustic frequency, 1kHz, in the temperature range of -150 to 150℃. It was found that when the spe-cimen was aged in the temperature range under the spinodal curve within the mis-cibility gap, the internal friction increases with an increase of the aging time andreaches a maximum value at a certain aging time which is shorter with a higheraging temperature. Two internal friction peaks which did not appear before theaging were observed above room temperature after a definite aging time. These arethe martensite transformation peak and the relaxation peak originating from thestress-induced movement of the twin boundaries. The former peak shifts towardhigher temperatures with an increase of the aging time, whereas the relaxationpeak appearing at 15℃, is independent of the aging time and temperature. The ac-tivation energy associated with the relaxation peak was found to be 0.56 eV whichis about the same as that of the relaxation peak in binary alloy containing 90wt-% Mn. It was also found that the hardness, strength and the brittleness of thespecimen increase when aged below the spinodal curve within the miscibility gap.The addition of Al enhances the strength but reduces the internal friction of thespecimen. A choice of suitable aging time and temperature can give an optimum com-promise of high strength and high internal friction. Analysis of experimental re-sults suggests that spinodal decomposition leads to Mn-rich zones in the specimenand thus causes the phase transformation and the change of mechanical propertiesof the specimen.