终冷温度对低屈强比复合析出强化钢组织与性能的影响

利用热模拟方法测定低屈强比复合析出强化钢不同速率冷却后的显微组织并绘制动态连续冷却转变曲线,然后对比了不同终冷温度下试验钢的力学性能,并利用光学显微镜、扫描电镜与透射电镜分析不同终冷温度对试验钢轧后显微组织的影响。结果表明,随冷却速度的增加,试验钢的组织由粒状贝氏体转变为板条贝氏体,未发现铁素体组织,具有高淬透性。随终冷温度由400 ℃升为450 ℃,钢中板条亚结构发生粗化,位错密度下降,但高温下合金元素快速扩散使富Cu相与Nb/Ti碳化物的数量提高,析出强化效果增强。经优化终冷温度为450 ℃,此时试验钢中粒状贝氏体比例较高,可获得高强度与低屈强比的良好匹配。     

采用外冷却生产厚大断面球铁铸件的试验研究

采用外冷却方法生产厚大断面球铁铸件的基础试验中，选用不同的冷却方式和冷却材料，进行试块冷却曲线对比，得出外冷材料的激冷效果。选用石墨冷铁，挂砂冷铁材料和综合通风、通水的外冷却方法，进行模拟试块冷却，获得了试块冷却曲线，外冷饮温度变化的曲线，用外冷却方法成功地生产了各种厚大断面球铁铸件。     

Q460C钢连续冷却转变规律研究

利用热膨胀法并结合金相-硬度法在热膨胀仪和Gleeble-1500热模拟试验机上测定了Q460C钢的未变形和变形条件下的连续冷却转变曲线.测定了转变后组织的维氏硬度,随冷速的提高,组织硬度增大.两种CCT曲线上均有铁素体区(F)、珠光体区(P)、贝氏体区(B)和马氏体区(M).变形使CCT曲线向左上方移动,提高了奥氏体冷却转变开始温度,随冷速加大提高得越多.变形扩大了F和P区,缩小了B和M区.与不含铌的16Mn钢的CCT曲线对比,分析了铌对连续冷却转变规律的影响.     

20MnSi棒材轧后分级水冷过程温度场有限元模拟

对20MnSi棒材轧后分级控制冷却过程温度场变化进行了有限元模拟仿真并与CCT曲线相结合,获得了棒材在分级控冷条件下温度-时间历程曲线及其组织变化特点,为优化控冷工艺方案提供了理论依据.     

金属凝固微观组织形成的数值模拟

依据金属凝固的基本理论,在Oldfield的连续形核和晶粒长大模型基础上,引入了时间因子,运用随机方法,建立了连续冷却条件下形核和生长的随机模型,使形核和生长模型函数与时间直接相关,反映了连续冷却条件下的金属凝固微观组织的演化过程。基于上述模型,编制了计算模拟程序,模拟了Zn-5Al共晶合金微观组织的凝固过程,并用试验结果对模拟结果进行了验证对比,模拟结果与试验结果基本相符。     

特厚矩形连铸坯二冷区冷却水的反算研究

针对700 mm×1 500 mm特厚矩形铸坯二冷制度的水量分配进行研究,根据经验公式初步确定二冷区各段的冷却水量,再由计算的铸坯表面目标温度曲线确定各二冷段的传热系数,并结合有限元仿真模拟,对比结果曲线验证方案的可行性。通过传热系数与水流密度的经验公式,确定各冷却段的水流密度值,最终对二次冷却水量进行优化。     

热轧螺纹钢化学剂冷却过程温度场的数值模拟及实验研究

本文对化学剂冷却热轧螺纹钢在两段式冷却(前段化学剂FM冷却+后段水冷)过程中的温度场进行了有限元模拟,并在实验室对前段化学剂FM冷却生成的氧化皮的耐蚀性能进行了评价.采用工业现场一段式水冷的工艺参数,模拟了一段式水冷的温度场.对比一段式水冷的温度场,分析了两段式冷却的工艺参数对冷却过程温度场的影响.结果表明,在前段化学剂FM冷却时,采用较小的对流换热系数,有利于提高前段化学剂冷却时的氧化温度,从而改善氧化皮的质量;在后段水冷时,在保持原一段水冷的对流换热系数的情况下,两段式冷却水冷段的冷却曲线与一段式水冷非常接近,能够满足Ⅲ级热轧螺纹钢的力学性能的要求.采用有限元模拟优化的工艺参数,在实验室模拟了前段化学剂FM冷却过程,获得了致密的氧化皮,其耐蚀性能显著优于水冷钢筋,说明采用前段化学剂冷却来改善水冷钢筋的耐蚀性能是可行的.     

奥氏体变形对一种Cr-Mo双相钢连续冷却相变的影响

利用Gleeble 3500热模拟试验机对一种Cr-Mo双相钢进行了奥氏体未变形和变形两种条件下的连续冷却相变测定试验,获得了两种试验条件下的连续冷却相变CCT曲线。对比分析了两种试验条件下获得的组织和连续冷却相变曲线,探讨了奥氏体变形对Cr-Mo双相钢连续冷却相变的影响。结果显示,奥氏体区变形明显提升了铁素体相变开始温度和珠光体相变临界冷却速度,使CCT曲线向左上方移动,同时,奥氏体区变形促进了贝氏体及马氏体的形成。     

冷却模式对Ti-Nb微合金高强钢组织和性能的影响

热轧后的冷却模式影响微合金高强钢的组织和析出,从而影响最终性能。在实验室对一种Ti-Nb微合金高强钢进行了前段快冷和后段快冷两种模式的热模拟试验,研究了冷却模式对Ti-Nb微合金高强钢组织和性能的影响。同时根据实验室研究结果,在国内某热连轧带钢厂对类似钢种进行了工业试验。结果表明:采用后段快冷模式,试样的晶粒尺寸(3.10μm)比前段快冷试样的晶粒尺寸(4.07μm)要小,且后段快冷试样析出物的体积分数(1.04%)比前段快冷试样析出物的体积分数(0.81%)大,后段冷却模式具有更好的细晶强化和析出强化作用。     

中厚板无约束淬火冷却过程温度场有限元模拟

针对中厚钢板无约束淬火冷却过程温度场变化情况,建立了钢板冷却二维传热过程数学模型,采用有限元分析方法,对钢板二维温度场进行了数值模拟,得到钢板在空冷-水冷-空冷返红条件下的温度-时间曲线、瞬态温度场分布、上表面与中心温差-时间曲线及上、下表面温差-时间曲线,为中厚钢板淬火冷却温度预测和控制提供了依据,为制定合理的淬火工艺提供了有力的指导。     

A357铝合金半固态流变压铸数值模拟

利用商业模拟软件Flow-3D对A357铝合金半固态流变压铸过程进行了研究。对不同压射压力和不同压射速度下的半固态流变充型流动状态及气孔分布进行了模拟,并对其凝固过程进行了模拟,最后通过试验对其进行验证。模拟及试验结果显示,随着压射压力与压射速度的增大,半固态熔体流动状态从层流向紊流过渡;同时压射压力和压射速度的增大对气孔分布也有一定的影响。模拟结果与试验结果基本保持一致,表明利用Flow-3D对压铸工艺进行参数优化是可行的,实现了压铸件性能提高的目的。     

冷却速率对A357合金凝固组织的影响

以不同冷却速率铸造A357合金试样,用光学显微镜和扫描电镜(SEM)分析其凝固组织.通过不同冷却速率下的DTA试验研究了A357合金的凝固行为;采用DSC试验研究了不同冷却速率所得试样中相的变化;测定了这些试样的微观硬度.结果表明,随着冷却速率的提高,A357合金的宏观晶粒尺寸和二次枝晶臂间距减小,共晶Si相的形态更加细小,且分布愈加弥散;合金液相线温度和二元共晶的反应温度降低,三元或四元共晶反应被抑制,合金凝固组织中Mg2Si相的析出受到抑制,微观硬度明显提高.     

几种车用铝合金的半固态成形工艺研究

研究了汽车件铝合金A357、ZL108和AS9U3半固态坯料制备与压铸成形工艺。试验分析比较了上述三种铝合金的兰固态非枝晶组织特点,结果显示：所制备的A357合金与国外专业公司生产的兰固态坯料组织比较接近ZL108和AS9U3合金的半固态组织与A357合金有显著区别,工艺优化,采用兰固态压铸技术成功地制成3种高质量的汽车零件。     

几种车用铝合金的半固态成形工艺研究

研究了汽车件铝合金A3 5 7、ZL10 8和AS9U3半固态坯料制备与压铸成形工艺。试验分析比较了上述三种铝合金的半固态非枝晶组织特点。结果显示 :所制备的A3 5 7合金与国外专业公司生产的半固态坯料组织比较接近 ,ZL10 8和AS9U3合金的半固态组织与A3 5 7合金有显著区别。通过工艺优化 ,采用半固态压铸技术成功地制成 3种高质量的汽车零件     

高剪切熔体处理下半固态A357合金浆料的组织特征研究

以A357铝合金为试验材料,利用双螺旋流变制浆设备进行了半固态浆料的制备工艺研究。考察了高剪切熔体处理,也即高强度的搅拌剪切和高强度的紊流作用下,搅拌速度和搅拌时间对铝合金非枝晶组织的形成以及组织特征的影响。结果表明:随着搅拌速度的提高,坯料组织中初生α-Al晶粒尺寸减小,形状变得圆整均匀,但是固相体积分数逐渐减小,搅拌速度的增大对球晶的生长起到了抑制作用;熔体在双螺旋设备中的凝固主要经历了连续冷却以及等温剪切两个过程,搅拌时间越长,晶粒越圆整均匀,尺寸越大,但晶粒密度会急剧下降,总的固相分数不会发生明显变化。     

Mechanical Performance of Cold-Sprayed A357 Aluminum Alloy Coatings for Repair and Additive Manufacturing

Cold-sprayed coatings made of A357 aluminum alloy, a casting alloy widely used in aerospace, underwent set of standard tests as well as newly developed fatigue test to gain an information about potential of cold spray for repair and additive manufacturing of loaded parts. With optimal spray parameters, coating deposition on substrate with smooth surface resulted in relatively good bonding, which can be further improved by application of grit blasting on substrate’s surface. However, no enhancement of adhesion was obtained for shot-peened surface. Process temperature, which was set either to 450 or 550 °C, was shown to have an effect on adhesion and cohesion strength, but it does not influence residual stress in the coating. To assess cold spray perspectives for additive manufacturing, flat tensile specimens were machined from coating and tested in as-sprayed and heat-treated (solution treatment and aging) condition. Tensile properties of the coating after the treatment correspond to properties of the cast A357-T61 aluminum alloy. Finally, fatigue specimen was proposed to test overall performance of the coating and coating’s fatigue limit is compared to the results obtained on cast A357-T61 aluminum alloy.     

Development of pressure control system in counter gravity casting for large thin-walled A357 aluminum alloy components

Counter gravity casting equipments（CGCE） were widely used to produce large thin-walled A357 aluminum alloy components. To improve the pressure control precision of CGCE to get high quality castings, a pressure control system based on fuzzy-PID hybrid control technology and the digital assembled valve was developed. The actual pressure tracking experiment results show that the special system by applying PID controller and fuzzy controller to varied phases, is not only able to inherit the small error and good static stability of classical PID control, but also has fuzzy control＇s advantage of fully adapting itself to the object. The pressure control error is less than 0.3 kPa. By using this pressure control system, large complex thin-walled A357 aluminum alloy castings with high quality was successfully produced.     

Heat transfer during quenching of modified and unmodified gravity die-cast A357 cylindrical bars

Heat transfer during quenching of chill-cast modified and unmodified A357 Al-Si alloy was examined using a computer-aided cooling curve analysis. Water at 60 °C and a vegetable oil (palm oil) were used as quench media. The measured temperatures inside cylindrical probes of the A357 alloy were used as inputs in an inverse heat-conduction model to estimate heat flux transients at the probe/quenchant interface and the surface temperature of the probe in contact with the quench medium. It was observed that modified alloy probes yielded higher cooling rates and heat flux transients. The investigation clearly showed that the heat transfer during quenching depends on the casting history. The increase in the cooling rate and peak heat flux was attributed to the increase in the thermal conductivity of the material on modification melt treatment owing to the change in silicon morphology. Fine and fibrous silicon particles in modified A357 probes increase the conductance of the probe resulting in higher heat transfer rates. This was confirmed by measuring the electrical conductivity of modified samples, which were found to be higher than those of unmodified samples. The ultrasound velocity in the probes decreased on modification.     

A357铝合金大型复杂薄壁构件的淬火温度场、残余应力及变形的有限元分析(英文)

基于ABAQUS软件,采用有限元模拟计算的方法对A357铝合金大型复杂薄壁构件的淬火过程进行研究。通过采用传统的反传热方法,对不同淬火介质在不同温度下的换热系数进行精确求解。精确的换热系数确保对A357铝合金大型复杂薄壁构件淬火过程中温度场预测的准确性。采用3种淬火介质(水、机油,5%-UCON淬火试剂A)。通过综合考虑淬火介质及温度因素,对薄壁构件的残余应力及变形的分布和大小进行有限元预测,得到构件淬火结束后的最大残余应力及变形。     

Effects of spray configuration on the uniformity of cooling rate and hardness in the quenching of aluminum parts with nonuniform shapes

The present study constitutes a step toward the understanding, and eventual optimization, of the spray quenching process for aluminum extrusions. A spray quenching test bed was constructed to simulate an industrial spray quench. This experimental facility allowed for the testing of irregular shapes using up to eight water sprays. Quenching experiments were conducted using flat water sprays in two different configurations with an L-shape testpiece constructed from commercially pure aluminum Al 1100-O. Section thickness and spray configuration were found to have a significant effect on the cooling rate and cooling uniformity. The commercially pure aluminum Al 1100-O L-shape and a similar L-shape constructed from aluminum alloy 2024-T6 were simulated with a two-dimensional finite-element code and spray correlations available from previous studies. Using the quench factor technique, the numerical simulation enabled the assessment of merits of different spray configurations with respect to the magnitude and uniformity of hardness of the 2024-T6 L-shape.