模壁润滑温压Fe-2Ni-2Cu-1Mo-1C材料的烧结行为研究

模壁润滑和温压的结合有利于提高材料的生坯密度和力学性能.我们主要研究了烧结温度(1 100～1 300℃)和烧结时间(40～80min)对模壁润滑温压Fe-2Ni-2Cu-1Mo-1C材料烧结行为的影响.模壁润滑采用聚四氟乙烯乳化液润滑.结果表明:经不同的温度下烧结50min,模壁润滑温压材料的烧结密度随烧结温度升高先增大后降低,烧结膨胀变化趋势刚好相反;在1300℃温度下烧结不同时间,模壁润滑温压材料的烧结密度随着烧结时间的延长先下降随后逐渐提高,而烧结尺寸变化趋势刚好相反.模壁润滑温压材料的抗拉强度和伸长率随烧结温度的提高或烧结时间的延长而增大;模壁润滑温压材料的拉伸性能是烧结温度和烧结时间的函数,抗拉强度和伸长率与烧结参数具有良好的线性回归关系.     

镁合金薄壳压铸件充型凝固与热应力数值分析

以镁合金航空仪表壳为例,建立三维模型和有限差分模型,通过数值模拟镁合金薄壳在高压铸造过程中的充型温度场、凝固过程温度场及凝固过程应力场。分析模拟结果发现:在压铸过程中铸件局部温降梯度大的部分容易引起凝固过程的不一致,导致铸件局部应力过大,加大铸件的热裂倾向,通过分析结果预测铸件裂纹发生的区域,预测结果与实际情况吻合,并对原工艺提出相应的改进措施。     

外浇包熔体温度对7075/6009铝合金铸锭组织和硬度分布的影响

采用双流浇注连续铸造技术制备了7075/6009铝合金铸件,重点研究了外浇包熔体温度对该复合材料铸锭的组织及铸锭横截面上成分和硬度分布的影响.结果表明:在其他工艺参数一定的情况下,外浇包熔体温度从720℃上升到760℃时,铸锭外层合金的平均厚度减少了14.3%,铸锭内层合金的平均二次枝晶间距由约15μm增加到20μm,铸锭外层合金的平均二次枝晶间距由约80μm增大到100μm,铸件内层合金和外层合金的硬度分别降低了8.5%和9.3%.     

船用柴油机活塞铸造顺序凝固工艺设计及数值模拟

在生产壁厚变化较大的复杂球墨铸铁零件中,仅依靠球墨膨胀难以消除铸件缩孔、缩松等缺陷。通过数值模拟,分析了某船用柴油机活塞铸造缩孔、缩松产生的成因。采用阶梯流道、冷铁及冒口布置建立了顺序凝固方案,并通过数值模拟及试验方法进行验证。结果证明,通过顺序凝固方案能够消除活塞缩孔、缩松缺陷。     

铝型材挤压成形过程金属流动状态的数值模拟

运用基于有限元法的模拟软件MSC.Marc对一复杂空心铝合金型材挤压过程进行数值模拟,在模拟过程中采用了一种既可以避免网格畸变和重划分,又能保证分析准确性的有限元模拟方法,研究了金属在模腔内的流动规律,利用出口质点轴向流速的SDV值定量的判定截面出口速度分布的均匀程度,揭示了金属的流动速度对产品形状及尺寸的影响,并将模拟仿真结果与试模结果进行比照分析,证明该方法可以成功地预测实际挤压过程中可能出现的潜在缺陷.     

低成本高比重细长钨钉配重零件的研制

本文采用传统的粉末冶金压制成形工艺,通过混料、压制、脱胶、烧结和机加工,可生产出完全符合要求的高比重细长钨钉零件。与注射成形工艺相比,简化了生产工艺,提高了生产效率,大大降低了生产成本,取得了良好的经济效益。     

温压技术中的致密化机制

根据聚合物的流动特性和粉末成形特点 ,试验研究了温压条件下金属粉末的塑性变形 ,理论分析了温压技术中的聚合物膜的成形和致密化机制。结果表明 :在压制初期 ,聚合物良好的流动性和较低的摩擦因数改善了金属粉末的充填行为。在压制末期 ,聚合物在金属表面形成一层微米或亚微米级薄膜。这层薄膜与基体结合牢固 ,将金属粉末与粉末隔离开来 ,促进粉末的塑性变形。     

Mechanical properties and tribological behavior of a cast heat-resisting copper based alloy

Mechanical properties and tribological behavior of a novel cast heat-resisting copper based alloy are investigated. The corresponding properties of a commercial aluminum bronze C95500 (ASTM B30) are compared with the alloy. The results show that the alloy possesses better mechanical properties and tribological behaviors than that of C95500 at elevated temperature. The tensile strength, elongation and hardness at 500℃ are 470MPa, 2.5% and HB220, respectively. The wear rate of the developed alloy at ambient and elevated temperature is about one-sixth and one-fortieth of that of C95500, respectively. The alloy is very suitable for ma-nufacturing heat-resisting and wear-resisting parts. Major strengthening mechanisms for the alloy are solution strengthening and the second phase strengthening.     

Sinter-hardening properties of partially-diffuse alloyed Fe-Cu-Ni-Mo-C material prepared by die wall lubricated warm compaction

The sinter-hardening properties of a partially-diffuse alloyed Fe-2Cu-2Ni- 1Mo- 1C material were investigated. Samples were formed by die wall lubricated warm compaction method, then, sintered in hydrogen atmosphere at 1 150 ℃ for 1 h and cooled at 4.6, 2.9 and 1.5 ℃/s, respectively, from 900 ℃ down to 600℃. Effects of cooling rate on mechanical properties and microstructure of the material were discussed. The results show that when the cooling rate increases, the tensile strength of the material increases, while, the elongation shows opposite result. The sintered material has a tensile strength of 872 MPa and an apparent hardness of HB 257 at a cooling rate of 4.6 ℃/s. Slight shrinkage is observed. Heterogeneous microstructures containing martensite, bainite, pearlite and nickel-rich retained austenite are observed in the material. Higher martensite content can be obtained at higher cooling rate, while, at lower cooling rate, pearlite and retained austenite dominated the microstructure.     

Die wall lubricated warm compaction of iron-based powder metallurgy material

Lubricant is harmful to the mechanical properties of the sintered materials,Die wall lubrication was applied on warm compaction powder metallurgy in the hope of reducing the concentration level of the admixed lubricant.Iron-based samples were prepared by die wall lubricated warm compaction at 175℃,using a compacting pressure of 550MPa.Emulsified polytetrafluoroethylene(PTFE) was used as die wall lubricant.Admixed lubricant concentration ranging from 0 to 0.5% was tested.Extremely low admixed lubricant contents were used.Results show that in addition to the decrease in ejection forces,the green density of the compacts increases with the decrease of admixed lubricant content until it reaches the maximum at 0.06% of lubrcant content,then decreases with the decrease of admixed lubricant content.The mechanical properties of the sintered compacts that contain more than 0.06% admixed lubricant are better than those of the samples that contain lesser lubricant.No scoring was observed in all die wall lubricated experiments.