GH4169高温合金的静态再结晶动力学

对GH4169高温合金在Gleeble-3500热模拟实验机进行了双道次和单道次热压缩实验。分析了变形温度、应变速率、间隔保温时间、变形量和初始晶粒尺寸对GH4169高温合金静态再结晶体积分数的影响。实验结果表明:变形温度越高、应变速率越大、道次间隔时间越长,变形量越大,初始晶粒度越小,静态再结晶体积分数越大。根据实验结果,建立了GH4169高温合金的静态再结晶模型,并将所建立的模型的预测结果和实验结果进行了对比分析,二者比较吻合。     

单驱动双滑块分型抽芯在铅套半热流道压铸模中的应用

针对合金密度较大的铅套,首次尝试使用半热流道模具的热室压铸机生产,以减少合金液在模具浇道流动过程中产生的裹气及压射能量损耗。设置直浇道热作件支撑机构,降低热作件以热传导方式在模具剩余部分的热损耗,满足了锥浇道浇口套与热流道热作件的互换性要求。模具采用周而复始和谐而自然的分型面离合装置,提高了模具使用的稳定性。在一模多腔压铸型中,提出了一种单驱动双滑块分型抽芯机构,使模具结构更加合理,可有效地减小模具尺寸。     

弧形盒的组合凹模设计和热压罐成型技术

通过分析弧形盒三处凸台和一处凹坑"障碍体"对模具脱模的影响,得出采用凹模横向一处分型为最佳方案的结论,设计成凹模结构。介绍了弧形盒热压罐成型技术。经生产实践证明,该模具结构合理,制件脱模顺利,加工的弧形盒质量优良。     

放电等离子烧结法和热压法制备的镀钛金刚石/铜多层复合材料的结构和热性能

采用放电等离子烧结技术(SPS)和热压法(HP)分别制备用于电子封装领域的多层镀钛金刚石/铜复合材料获得。借助扫描电子显微镜(SEM)分析了复合材料的显微组织,同时对热导率(TC)和热膨胀系数(CTE)等热性能参数进行了分析。层状复合材料的热导率理论值参考改良的哈塞尔曼-约翰逊(HJ)模型,同时考虑TiC界面的影响计算,结果为446.66 W·(m·K)~(-1),而热膨胀系数则通过热膨胀仪测试确定。结果显示,经放电等离子烧结的试样与经热压制备的试样相比,缺陷相对较少,界面的结合对于复合材料热导率的影响十分明显。提出了一个界面影响的模型示意图,热导率随着碳化物层厚度的增加和气孔的出现而减小。由此可见,实现高热导率的条件是复合材料中的碳化物层较薄、同时没有气孔的出现。     

网孔结构La2Sn2O7粉体的制备及其在Ag-电接触材料的制备及性能研究

以五水四氯化锡和硝酸镧为原料,采用化学共沉淀法在烧结温度920℃条件下合成了锡酸镧粉体。通过高能球磨法+成型烧结工艺制得Ag-La₂Sn₂O₇电接触复合材料。重点考察了胶凝剂浓度、烧结工艺对La₂Sn₂O₇粉体形貌及物相的影响,并对Ag- La₂Sn₂O₇电接触材料的物理性能进行了分析。研究结果表明：以碳酸氢铵为胶凝剂,于烧结温度920℃,2h条件下获得具有网孔结构的La₂Sn₂O₇粉体;于成型压力1200MPa,烧结温度900℃,6h条件下制得的Ag-La₂Sn₂O₇电接触材料表现出较佳的电阻率和硬度值。经过热挤压工艺,Ag-La₂Sn₂O₇电接触材料发生了大塑性变形,颗粒在热挤压过程中发生流动变形,形成类纤维状结构的排列分布状态,表现出更低的电阻率。     

高应变速率对690合金热变形及可挤性的影响

利用Gleelbe热模拟实验以及有限元分析了高应变速率对690合金热变形行为以及挤压可行性的影响,并根据实验和有限元结果进行挤压。结果表明：690合金的流变应力对应变速率均较敏感;大于10 s_-1 的高应变速率下,变形温升显著上升;再结晶晶粒尺寸在低应变速率下,随应变速率的升高而降低,高应变速率则随应变速率的增加而增大;挤压时,最大挤压力随着应变速率的上升先降低再升高;根据实验以及有限元计算结果,成功挤出了合格的690管材。     

Effect of deformation mode,dynamic recrystallization and twinning on rolling texture evolution of AZ31 magnesium alloys

In order to obtain quantitative relationship between (0002) texture intensity and hot rolling conditions, conventional rolling experiments on AZ31 magnesium alloys were performed with 20%–40% reductions and temperatures within the range of 300–500 °C. Shear strain and equivalent strain distributions along the thickness of the rolled sheets were calculated experimentally using embedded pin in a rolling sheet. Rolling microstructures and textures in the sheet surface and center layers of the AZ31 alloys were measured by optical microscopy (OM), X-ray diffractometry (XRD) and electron back scatter diffraction (EBSD). Effects of the rolling strain, dynamic recrystallization (DRX) and twinning on the texture evolution of the AZ31 alloys were investigated quantitatively. It is found that the highest (0002) basal texture intensities are obtained at a starting rolling temperature of 400 °C under the same strain. Strain–temperature dependency of the (0002) texture intensity of the AZ31 alloy is derived.     

Quality index and hot tearing susceptibility of Al–7Si–0.35Mg–xCu alloys

The effects of Cu addition (0.5%, 1%, 1.5%, 2%, and 3%, mass fraction) on the quality index (Q_i) and hot tearing susceptibility (HTS) of A356 alloy were investigated. According to the results, Cu addition up to 1.5% increases the Q_i by almost 10%, which seems to be due to its solid solution strengthening and dispersion hardening effect of Cu-rich Al₂Cu and AlMgCuSi compounds. However, further addition of Cu (up to 3%) decreases the Q_i by almost 12%, which is likely due to the reduction of tensile strength and elongation caused by increased volume fraction of brittle Cu-rich intermetallics and microporosities in the microstructure. It is also found that Cu increases the HTS of A356 alloy measured by constrained rod casting method. According to the thermal analysis results, Cu widens the solidification range of the alloy, which in turn, decreases its fluidity and increases the time period during which the mushy-state alloy is exposed to the hot tearing susceptible zone. SEM examination of the hot tear surfaces in high-Cu alloys also demonstrates their rough nature and the occurrence of interdendritic/intergranular microcracks as convincing evidences for the initiation of hot tears in the late stages of solidification in which there is not enough time for crack healing.     

Prediction on hot deformation behavior of spray-formed 7055 aluminum alloy via phenomenological models

Hot compression tests in the temperature range of 340–450 °C and strain rate range of 0.001–1 s^?1 of spray-formed 7055 aluminum alloy were carried out to study its hot deformation behavior. Three phenomenological models including Johnson–Cook, modified Fields–Backofen and Arrhenius-type were introduced to predict the flow stresses during the compression process. And then, a comparative predictability of the phenomenological models was estimated in terms of the relative errors, correlation coefficient (R), and average absolute relative error (AARE). The results indicate that Johnson–Cook model and modified Fields–Backofen model cannot well predict the hot deformation behavior due to the large deviation in the process of line regression fitting. Arrhenius-type model obtains the best fit through combining the effect of strain rate and temperature.     

低碳铝镇静钢热镀锌表面粗晶缺陷形成原因及对策

低碳铝镇静钢热镀锌板表面易产生"指甲印"缺陷,缺陷主要分布在整卷带钢带中1/3长度位置、带钢表面中间位置。通过金相观察可以确认缺陷处因晶粒明显长大,形成粗晶,晶界处开裂表现为"指甲印"缺陷。低碳铝镇静钢在热轧工序生产时的卷取温度为730℃,这个温度恰好处于A_1温度以上,卷取后带钢仍处在奥氏体和铁素体两相区。在卷取后,带中1/3位置散热较慢,温度保持在A_1线以上,奥氏体晶粒在此温度下继续长大,形成粗大晶粒。在冷轧工序的生产过程中,带钢表面受压应力和切应力作用,粗大的晶粒沿边界开裂,表现为"指甲印"缺陷。通过降低热轧卷取温度,使带钢卷取后的温度处于A_1线以下,带钢组织由铁素体和渗碳体组成,使带钢晶粒在卷取后冷却的过程中不再长大形成粗晶,消除了低碳铝镇静钢热镀锌带钢表面"指甲印"缺陷。