Effect of heat treatment on microstructures and mechanical properties of sand-cast Mg-4Y-2Nd-1Gd-0.4Zr magnesium alloy

Influence of heat treatment on the microstructures and mechanical properties of sand-cast Mg-4Y-2Nd-1Gd-0.4Zr magnesium alloy was investigated,and the tensile fracture mechanisms of the studied alloys under different conditions were also discussed.The results show that the optimum T4 and T6 heat treatment conditions for the as-cast Mg-4Y-2Nd-1Gd-0.4Zr alloy are 525°C,8 h and（525°C,8 h）＋（225°C,16 h）,respectively,with regard to the microstructure observation,DSC heating curve and mechanical properties.The hardness,yield strength,ultimate tensile strength and elongation of the Mg-4Y-2Nd-1Gd-0.4Zr alloy treated by optimum T6 heat treatment are HV91,180 MPa,297 MPa and 7.4%,respectively.Moreover,the Mg-4Y-2Nd-1Gd-0.4Zr alloys under different heat treatment conditions exhibit different tensile fracture modes.

Influence of pouring temperature on solidification behavior, microstructure and mechanical properties of sand-cast Mg-10Gd-3Y-0.4Zr alloy

Influence of the pouring temperature ranging from 680 to 780 ℃ on the solidification behavior, the microstructure and mechanical properties of the sand-cast Mg-10Gd-3Y-0.4Zr alloy was investigated. It was found that the nucleation undercooling of the a-Mg phase increased from 2.3 to 6.3 ℃. The average a-Mg grain size increased from 44 to 71 μm, but then decreased to 46 μm. The morphology of the eutectic compound transformed from a continuous network into a discontinuous state and then subsequently into an island-like block. The volume fraction of β-Mg_24RE_5 phase increased and its morphology transformed from particle into rod-like. The increase in pouring temperature increased the solute concentration. YS increased from 138 to 151 MPa, and UTS increased from 186 to 197 MPa. The alloy poured at 750 ℃ had optimal combining strength and ductility. The fracture surface mode transformed from quasi-cleavage crack into transgranular fracture, all plus the dimple-like fracture, with the micro-porosity and the re-oxidation inclusion as major defects. The average a-Mg grain size played a main role in the YS of sand-cast Mg-10Gd-3Y-0.4Zr alloy, besides other factors, i.e. micro-porosity, morphology of eutectic compounds, re-oxidation inclusion and solute concentration.

Influence of cooling rate on solidification behavior of sand-cast Mg-10Gd-3Y-0.4Zr alloy

The effect of the cooling rate ranging from 1.4 °C/s to 3.5 °C/s on the solidification behavior of the sand-cast Mg?10Gd?3Y?0.4Zr alloy was studied by computer aided cooling curve analysis (CA-CCA). With the increase in cooling rate, the nucleation temperature (Tα,N) increases from 634.8 °C to 636.3 °C, the minimum temperature (Tα,Min) decreases from 631.9 °C to 630.7 °C, the nucleation undercooling (ΔTN) increases from 2.9 °C to 5.6 °C, the beginning temperature of the eutectic reaction (Teut,N) increases, the time of the eutectic reaction shortens, solidus temperature decreases from 546.0 °C to 541.4 °C, and solidification temperature range (ΔTS) increases by 6.1 °C. The increased nucleation rate (N&) is supposed to be the main reason for the increased?TN. Increased value (Teut,N?Teut,G) and shortened time of the eutectic reaction cause the change in the volume fraction and morphology of the second phase.

Effect of complex melt-refining treatment on microstructure and mechanical properties of sand-cast Mg–10Gd–3Y–0.5Zr alloy

The effect of complex melt-refining treatment （melt flux incorporating with rotating gas bubble stirring） on microstructure and mechanical behavior of the sand-cast Mg-10Gd-3Y-0.5Zr alloy was investigated. In addition, the melt purifying mechanism of the complex melt-refining treatment for the sand-cast alloy was discussed systematically. The results show that the new melt-refining method can significantly improve melt quality and mechanical behavior of the tested alloy, i.e., compared to the reference unpttdfied alloy, the volume fraction of inclusions decreased from 0.47% to 0.28%, the ultimate tensile strength and elongation for T6-treated alloy increased from 245 MPa and 0.7% to 312 MPa and 4.5%, respectively. Especially, combining 1% flux with rotating gas bubble stirring can get even better purifying effectiveness than conventional sole 2% flux purification; the use of melt flux decreased by 50% and significantly reduced environmental pollution.

Microstructure and mechanical properties of repair welds of low-pressure sand-cast Mg?Y?RE?Zr alloy by tungsten inert gas welding

The sand castings of Mg-Y-RE-Zr series alloys are widely utilized in the large scales and complex shapes in the aerospace industry,as a result of which there are always some cast defects in the products. In this study, the feasibility of repair welding of sand-cast Mg-4 Y-3 RE-0.5 Zr alloy by tungsten inert gas(TIG) welding was scrutinized with different welding currents from 150 to 210 A. The results indicated that defect-free repaired joints with good appearance could be acquired at 170 and 190 A. Interestingly, the grain size of the fusion zone(FZ) was refined initially and then increased with the linear increment of welding current. Because at the higher heat inputs, although the cooling rate of the molten pool was reduced, substantial constitutional supercooling for the grain refinement was attained after the Zr particles were transformed into Zr solutes. The tensile strength of the repaired joint at 170 A was 195 MPa with the maximum joint efficiency of 87.8%, and the elongation reached to 124.4% of the sand-cast base material(BM). However, serious grain coarsening and continuous eutectic structures generated in heat-affected zone(HAZ) above 190 A resulted in the weakening of the joint due to the brittle intergranular fracture.

Effect of heat treatment on the microstructures and mechanical properties of the sand-cast Mg-2.7Nd-0.6Zn-0.5Zr alloy

The tensile testing bars of the Mg-2.7Nd-0.6Zn-0.5Zr(wt.%)alloy were prepared by sand casting.The effect of solution temperature and aging time on the microstructures and mechanical properties were investigated.The as-cast alloy was composed ofαmagnesium matrix and Mg12Nd eutectic compounds.After solution treatment at 500℃ for 18 h,the volume fraction of eutectic compounds decreased from∼7.8%to∼2.3%,and some small Zr-containing particles were observed to precipitate at grain interiors.As the solution temperature increased to 525℃ for 14 h,most of the eutectic compounds dissolved into the matrix.Peak-aged at 200℃ for 12 h,fineβ″particles was the dominant strengthening phase.The yield strength,ultimate tensile strength and elongation in the peak-aged condition were 191 MPa,258 MPa and 4.2%,respectively.Moreover,the Mg-2.7Nd-0.6Zn-0.5Zr alloys under different heat treatment conditions exhibited different tensile fracture modes.

Microstructure,mechanical properties and fracture behaviors of large-scale sand-cast Mg-3Y-2Gd-1Nd-0.4Zr alloy

In order to improve the ductility of commercial WE43 alloy and reduce its cost,a Mg-3Y-2Gd-1Nd-0.4Zr alloy with a low amount of rare earths was developed and prepared by sand casting with a differential pressure casting system.Its microstructure,mechanical properties and fracture behaviors in the as-cast,solution-treated and as-aged states were evaluated.It is found that the aged alloy exhibited excellent comprehensive mechanical properties owing to the fine dense plate-shapedβ'precipitates formed on prismatic habits during aging at 200℃for 192 hrs after solution-treated at 500℃for 24 hrs.Its ultimate tensile strength,yield strength,and elongation at ambient temperature reach to 319±10 MPa,202±2 MPa and 8.7±0.3%as well as 230±4 MPa,155±1 MPa and 16.0±0.5%at 250℃.The fracture mode of as-aged alloy was transferred from cleavage at room temperature to quasi-cleavage and ductile fracture at the test temperature 300℃.The properties of large-scale components fabricated using the developed Mg-3Y-2Gd-1Nd-0.4Zr alloy are better than those of commercial WE43 alloy,suggesting that the new developed alloy is a good candidate to fabricate the large complex thin-walled components.

Effects of substitution of Nd in a sand-cast Mg-2.5Nd-0.6Zn-0.5Zr alloy with x wt.% Sm(x=2.5, 4, and 6)

The microstructures and mechanical properties of a series of sand-cast Mg-Sm-Zn-Zr alloys under ascast, solution-treated and peak-aged states were thoroughly investigated. The OM, XRD, SEM and HRTEM were employed to characterize the microstructural evolution. The results indicate that substitution Nd in the conventional Mg-2.5 Nd-0.6 Zn-0.5 Zr alloy with different contents of Sm has comparative grain refinement effect and will fully change the dominant intermetallic phase. In addition, the substituted alloys perform clearly higher strength with comparative ductility at both as-cast and peakaged conditions and much greater aging hardening response than the referential alloy. It is obvious that the strength increments of this alloy are attributed to the changes of the eutectic intermetallic particles on grain boundaries.

一种叉车支架铸件的铸造工艺改进

某重型叉车支架属于叉架类构件,两侧对称,但壁厚不均匀,材质为球墨铸铁,经潮模砂高压造型工艺生产。分析铸件结构特点,采用中间注入式浇注方案,分型面为铸件中心平面,采用magma数值模拟软件对工艺方案进行模拟和优化。针对生产过程中的缩孔、缩松等缺陷和本体性能不足等问题,分别通过调整冒口尺寸、增加冷铁和优化铁液成分等措施,最终获得了内部致密、性能满足使用要求的铸件。

高圆形度人工硅砂在铸钢件造型工艺中的应用

鉴于铸钢用天然硅砂受国家资源保护的影响日渐稀缺,人工硅砂替代天然硅砂将是未来发展趋势。简单介绍了高圆形度人工硅砂生产工艺流程、主要技术指标、角形因数、破损率以及在铸钢件造型工艺中的应用情况,并与天然硅砂进行了对比。对比结果显示:人工硅砂可替代天然高硅砂应用于铸钢件的造型,也可替代进口硅砂在砂型3D打印技术中应用。

基于数值模拟的QT500-7固定底座砂型铸造工艺优化研究

采用三维绘图软件绘制QT500-7固定底座三维模型,分析其结构特点、工艺要求和服役条件等要素,初步设计了该球墨铸铁件的铸造工艺方案,并利用仿真模拟软件进行了充型和凝固收缩模拟研究。初始铸造工艺方案模拟结果表明,充型完整,无浇不足、冷隔等现象,但在铸件底板处厚大部位存在缩孔缺陷。通过增设冒口、冷铁来优化铸造工艺方案,显著提高铸件质量,在铸件内部已无缺陷显现,可为固定底座的实际铸造工艺设计提供参考。

铁路机车铸钢件造型制芯生产工艺优化

原采用普通水玻璃砂为面砂和湿型砂为背砂的双砂造型,普通水玻璃砂制芯的生产工艺生产机车铸钢件。由于普通水玻璃砂水玻璃的加入量高、型芯溃散性差、铸件清理困难,湿型砂在遇高温金属液后,会产生大量的气体,极易使铸件产生气孔及冷裂纹等铸造缺陷,决定对造型和制芯工序进行优化,开发酯硬化水玻璃砂造型、改性水玻璃砂制芯工艺,替代原有的机车铸钢件生产工艺。通过实际生产验证,结果表明采用新的工艺方法生产铸钢件可以满足机械化生产需求,提高产品质量,降低工人劳动强度,改善作业环境。

一种奥氏体不锈钢的四缸柱塞泵的铸造工艺研发

四缸柱塞泵奥氏体不锈钢铸件具有耐低温、壁厚均匀、结构复杂等特点,通过3DP砂型成型的工艺方法,对其进行了铸造工艺设计,包括冒口设计、冷铁设计、浇注系统设计、砂型设计及砂芯的一体化集成设计,应用先进的计算机CAE模拟软件优化铸造工艺,提高产品的质量,达到验收标准。

高液压射台前板球墨铸铁件铸造工艺设计

射台前板是注塑机中的关键部件之一,其油缸孔部位加工精度高且有承压要求。本文介绍了高液压球墨铸铁射台前板铸件的工艺难点,设计了分型方案、浇注系统及冷却系统,并借助软件模拟分析了缩孔与缩松缺陷,确定了型芯方案。通过合理选择铸件的化学成分,严格控制球化、孕育及浇注过程,铸件本体渗透检验(PT)达到EN1371标准的质量等级I级,附铸试块铸件的力学性能和金相组织均符合客户标准。

基于STL模型的砂型表面网格重构算法

为解决通用模拟软件对STL模型生成表面网格时存在局部网格稀疏的问题,本文提出了一种基于STL模型的砂型表面网格重构算法。该算法对生成的表面网格进行特征边界以及表面网格内部加密,可有效解决表面网格密度低、质量不高的问题。基于ProCAST模拟软件进行实例仿真,其结果验证了经表面网格重构后的STL网格模型模拟仿真的可行性。

改性铸造废砂对混凝土力学及耐磨性能的影响

用水玻璃对铸造废砂进行了改性处理,研究了改性铸造废砂的掺量(0、10%、30%、50%、70%)对混凝土力学性能和耐磨性能的影响。结果表明:随着改性铸造废砂掺量的增加,试件的28 d抗压强度先增大后减小,最佳掺量为10%;随着改性铸造废砂掺量的增加,试件的28 d弹性模量和磨耗量降低,说明弹性变形能力变大,耐磨性能提高。

基于数值模拟的通海阀铜合金铸件工艺优化

针对某船舶通海阀在铸造过程中易产生缩孔、缩松等缺陷问题,以Cu-7Ni-7Al-4Fe-2Mn合金通海阀铸件为研究对象,使用三维制图软件UG构建了铸件3D模型,并结合通海阀铸件的结构特性,设计了底注式浇注系统。利用数值模拟软件模拟了铸件的砂型铸造过程,分析了可能出现缩孔、缩松缺陷的位置,优化了通海阀铸件的浇注系统。研究了浇注温度、浇注时间、铸型预热温度等参数对铸件缩孔、缩松率的影响规律,结合正交试验方法优化出匹配的铸造工艺参数。研究结果表明,工艺参数对通海阀铸件缩孔率的影响程度从大到小依次是浇注时间、铸型预热温度、浇注温度。优化后的工艺参数分别为浇注温度1 200℃,浇注时间30 s,铸型预热温度35℃。通过在铸造缺陷较多的部位增大冒口尺寸,有效减少了缩孔、缩松铸造缺陷的产生。

高压蒸汽室铸钢件砂型铸造工艺模拟研究

基于高压蒸汽室铸钢件的结构特点和铸造工艺要求,设计了该铸钢件的砂型铸造初步方案,并采用ProCAST软件进行了充型和凝固收缩数值模拟研究。结果表明:充型过程平稳,未出现浇不足现象,但在蒸汽室底座厚大部位、蒸汽室顶部凸台处出现了大体积缩孔,同时铸件中产生了分散的缩松缺陷。结合模拟结果,对缺陷部位增加了冒口和冷铁,改进后的模拟结果良好,没有缩孔缺陷。

铸造工艺数据驱动的工程机械铸件缺陷预测

针对砂型铸造过程缺陷难以寻因、工艺数据类别不平衡问题,提出了一种基于特征重分布与代价敏感学习的卷积神经网络缺陷预测方法。首先,根据样本特征相关性,对特征向量排列顺序进行了优化;其次,基于不平衡工艺数据样本设计了代价敏感正则项,对模型损失函数进行了修正;最后,构建了缺陷预测模型(FR-CS-CNN)。测试结果表明,本研究构建的FR-CS-CNN在总体预测精度上达到了93.67%,相比卷积神经网络提升了2.96%。

SMOTE数据预处理算法在砂型铸造复杂铸件缺陷预测中的应用

针对实际生产过程采集的复杂转向桥铸件工艺数据中冷隔、气孔、砂眼、缩孔等缺陷类别的数据量严重不平衡、复杂铸件缺陷预测模型准确率不高的问题,结合砂型铸造实际工况,引入了SMOTE(Synthetic Minority Oversampling Technique)数据预处理算法,探究其在砂型铸造复杂铸件缺陷预测中的应用。根据采集到的复杂铸件不平衡数据集的特点,基于SMOTE数据预处理算法,科学扩充了不平衡数据集,创建了可用于训练复杂铸件缺陷预测模型的平衡数据集,数据预处理前后的模型预测准确率从86.50%提高至97.91%。