Influences of complex modification of P and RE on microstructure and mechanical properties of hypereutectic Al-20Si alloy

P and RE complex modification of hypereutectic Al-Si alloys was conducted. The influences of P, RE content on the microstructure and mechanical properties of alloys were investigated. The complex modifications of P and RE make the coarse block primary silicon obviously refined and the large needle eutectic silicon modified to the fine fibrous or lamella ones. P mainly refines the primary silicon, but excess P is unfavorable to the refinement of primary silicon. RE can well refine the primary and eutectic silicon, but its modification effect on the eutectic silicon is more obvious. P can repress the modification of RE on the eutectic silicon. The alloys with the additions of 0.08% P and 0.60% RE have the optimal microstructure and the highest mechanical properties. Compared with the unmodified alloy, the primary silicon of alloys can be refined from 66.4 μm to 23.3 μm and the eutectic silicon can be refined from 8.3 μm to 5.2 μm. The tensile strength is improved from 256 MPa to 306 MPa and the elongation is improved from 0.35% to 0.48%.

Effect of Cr and isothermal holding temperature on microstructure and properties of complex phase steel with high formability(CH steel)

The effects of Cr contents(0.3 and 1.0 wt.%)and isothermal holding temperatures(400,440,and 480℃)on the microstructure evolution and properties of complex phase steel with high formability(CH steel)were investigated using dilatometry,scanning electron microscopy,transmission electron microscopy(TEM),and X-ray diffraction.The results show that the microstructures of CH steel with 0.3 wt.%Cr are ferrite,granular bainite,martensite,and retained austenite,while no ferrite is observed in the microstructure of CH steel with 1.0 wt.%Cr in the same process.Cr promotes the precipitation of(Nb,Ti)C in the high-temperature austenite region through theoretical calculations and TEM observations.Cr retards the bainite transformation and refines the grain size of CH steel.Furthermore,as isothermal holding temperature increases from 400 to 480℃,the bainite and retained austenite fractions of two CH steels decrease,while the martensite fraction increases in the steels after final quenching.Consequently,the strength has an increasing tendency and the total elongation has a decreasing tendency with increasing isothermal temperature.

Microstructure and mechanical properties of lightweight Ti_(3)Zr_(1.5)NbVAl_(x)(x=0,0.25,0.5 and 0.75) refractory complex concentrated alloys

Combining high strength and good ductility is an urgent requirement for traditional structural materials,but yet a challenge.Newly emerging ductile Ti_(3)Zr_(1.5)VNbAl_(x)(x=0,0.25,0.5,0.75) refractory complex concentrated alloys(RCCAs) with high specific strength were designed and synthesized via vacuum arc-melting.Alloying effects of Al on microstructure and mechanical properties were systematically investigated.It was found that the phase composition in this alloy system changes from the single disordered body-centered cubic(BCC) phase to a nano-scale mixture of co-continuous disordered BCC and ordered B2 phases with the increase of Al concentration.This structure transition results in a remarkable increase in the yield strength of the RCCAs,i.e.,from 790 to 1118 MPa,leading to a superior specific yield strength of 199.4 MPa cm^(3)g^(-1)for the Al0.75 alloy,meanwhile,the tension plasticity maintained at~10%.TEM observation demonstrates that cell-forming structure and HDDWs induced by wave slip play a crucial role of considerable plasticity in Al0.25 alloy,whereas in Al0.5 alloy,microbands induced by planar slip dominant deformation behavior.The current work is important not only for providing novel high strength and tough structural materials with low density,but also sheds light on designing highperformance lightweight alloys with tunable microstructure.

选区激光熔化成形TiB_(2)/Al-Si-Mg大尺寸复杂构件

选区激光熔化(SLM)成形大尺寸复杂构件厚度多样、成形高度较高、方向复杂,需要研究构件微观组织均匀性和力学性能稳定性。本文以SLM成形TiB_(2)/Al-Si-Mg复合材料为研究对象,分析复合材料多级微观组织,对比不同成形厚度、高度、方向下复合材料的力学性能。结果表明:复合材料表现出熔池特征结构,细小等轴晶粒组织均匀分布且随机取向,纳米TiB_(2)颗粒在材料内部弥散分布。随成形厚度增加,复合材料伸长率保持稳定,抗拉强度受本征热处理影响略微增大;在不同成形高度下,复合材料抗拉强度和伸长率保持稳定;在不同成形方向下,复合材料抗拉强度保持稳定,伸长率受熔池结构影响在水平方向略高。基于以上结果,成功制备大飞机舱门铰链臂(588 mm×318 mm×470 mm)复杂结构件。

复合活化对废弃混凝土再生微粉活性的影响及机理研究

再生微粉具有潜在活性,可作为辅助性胶凝材料取代水泥,但活性低限制了其应用。采用物理-化学复合活化方法激发再生微粉的活性,研究了活化再生微粉的活性指数、力学性能和微观形貌。结果表明:随着研磨时间的延长,胶砂的抗压、抗折强度先提高后降低;当研磨时间为4 h时胶砂试块的28 d抗压强度为28.6 MPa,28 d活性指数为64.3%。采用物理-化学复合活化时,当研磨4 h且掺加1%Na2SO4+1%Ca(OH)2激发剂时,胶砂28 d抗压强度为35.2 MPa,28 d活性指数达到79.1%,再生微粉的活性显著提高。

CP1180镀锌复相钢电阻点焊焊接特性研究

针对板厚1.5 mm的CP1180镀锌复相钢进行电阻点焊试验,研究了接头金相组织、力学性能和电极寿命等焊接特性。结果表明,试验钢板电阻点焊的焊接电流窗口为2.4 kA。上限电流产生的焊核直径可达7.74 mm,焊核组织为板条马氏体。临界热影响区马氏体晶粒细小导致显微硬度升高,亚临界热影响区经历回火软化导致显微硬度降低。上限电流焊点的最大剪切力和最大正拉力分别为27.4 kN和9.8 kN,失效模式均为“纽扣”断裂。以上限电流焊接2000点,焊核直径始终大于最小焊核尺寸,电极使用寿命<2000点。

P-RE对过共晶Al-Si合金组织和性能的影响

采用P和RE对过共晶Al-Si合金进行复合变质处理,在不同P和RE添加量下对合金显微组织和力学性能进行了分析和测量。结果表明,P和RE复合变质对初晶硅和共晶硅均有很好的变质效果,初晶硅尺寸明显减小且棱角钝化,共晶硅由原来的长针状变为颗粒状。加入(质量分数,下同)0.08%P和0.6%RE时,合金的微观组织和力学性能同时达到最佳,室温和高温抗拉强度分别达到306MPa和187MPa,与未变质合金相比,提高了20%和34%;室温和高温伸长率分别达到0.48%和1.58%,与未变质合金相比,提高了40%和88%。

复合脱氧剂对钢力学性能影响的研究

研究了采用不同脱氧和变性剂处理钢水对钢力学性能的影响 ,特别是对车轮钢冲击性能的影响。分析了采用 Ba、Ca类合金变性处理时组织结构和晶粒的变化。结果表明 ,用 Si- Ca- Ba处理的钢材 ,其组织结构。

镁合金正挤压-弯曲剪切复合连续变形工艺及挤压力计算

结合传统挤压与弯曲剪切变形的特点提出一种棒-板正挤压-弯曲剪切复合连续变形新工艺,该工艺既可显著细化晶粒又可以弱化织构,极大地改善镁合金的综合力学性能。通过分析该复合变形方式的特点,建立了总挤压力数学模型,对正挤压-弯曲剪切复合成形所需的挤压力进行了系统、完整、准确的表征。根据各分区的变形特点,把实际的正挤压模型类比成等效面积的圆棒挤压模型,并引入形状复杂系数,利用上界法得出各分区的挤压力解析表达式,基于有限元数值模拟对形状复杂系数进行分析求解。最后通过与实验结果的比较得出该模型计算的结果与实际值的误差在5%的范围内,满足工程计算要求。

复合变形制备超细晶工业纯钛的研究进展

随着经济的发展和人口老龄化的加剧,医用金属材料在创伤外科、整形手术和口腔医疗中的需求量越来越大。其中钛及钛合金具有优异的耐腐蚀性能和良好的生物相容性,因此被广泛应用。钛合金中含有对人体有害的合金元素,会使人体出现病症,因此不含合金元素的工业纯钛在生物医学材料领域越来越受到重视。近几十年来,国内外学者应用等径通道挤压(ECAP)技术成功制备出超细晶工业纯钛。但是ECAP技术制备超细晶材料存在细化和强化极限,而且ECAP道次数较多,工序复杂,生产效率低,对工件的尺寸和形状要求很高,因此限制了超细晶工业纯钛的应用。为了使工业纯钛的强度满足使用要求,并且开发出易于实际运用的加工技术,将ECAP与传统塑性加工相结合(复合变形技术)的研究和应用越来越多。工业纯钛先经多道次ECAP变形细化晶粒,再经传统塑性加工提高位错密度,其强度可增加到1000 MPa左右,并且保持良好的塑性。后变形使ECAP变形后的等轴晶粒被拉长,且分布不均匀,材料的力学性能表现出强烈的各向异性。复合变形可以运用较少道次的ECAP,缩短了加工周期。此外,通过后变形可以将材料加工成所需的成品形状,更易于生产和应用。复合变形后的超细晶工业纯钛进行低温退火可以提高材料的塑性,得到更优的综合力学性能。本文综述了复合变形制备超细晶工业纯钛的研究进展,分别对不同复合变形后工业纯钛的显微组织、力学性能、热稳定性和织构演变进行了介绍。对复合变形制备超细晶工业纯钛过程中存在的问题和今后的研究方向进行了总结和展望,以期为开发高效率易加工的复合变形技术提供参考。

La、Pr复合变质铸造Al-Cu合金的力学性能研究

研究了La、Pr复合变质对铸造Al-Cu合金的时效硬度、室温力学性能和高温力学性能的影响,并探讨了稀土变质Al-Cu合金的作用机理。结果表明,随着时效温度的升高,未变质和复合变质的Al-Cu合金的峰值硬度都呈现逐渐降低的趋势;在同一时效温度下,Al-Cu合金峰值硬度从高至低顺序依次为:0.2%La+0.1%Pr变质合金>0.15%La+0.15%Pr变质合金>0.1%La+0.2%Pr变质合金>未变质合金;三种不同复合变质Al-Cu合金的室温抗拉强度和断后伸长率都要高于未变质处理的Al-Cu合金,且0.2%La+0.1%Pr复合变质的Al-Cu合金取得了最佳的强度与塑性结合。0.2%La+0.1%Pr复合变质的Al-Cu合金的高温性能优于未变质Al-Cu合金。La和Pr复合变质可以使Al-Cu合金的铸态组织得到有效细化;0.2%La+0.1%Pr复合变质Al-Cu合金在固溶时效处理后,θ'析出相的平均尺寸要比未变质Al-Cu合金小,且数量明显增多。

加钒合金化方法对钢筋组织性能的影响

研究了加钒铁合金直接合金化、加五氧化二钒和钒球还原合金化方法下,钒对400MPa级热轧带肋钢筋的组织、力学性能、夹杂物、析出物等的影响。结果表明：钒含量为0.06%~0.08%,钢筋各项力学性能指标均能达到GB1499-98标准要求;加钒合金化方法对钒的析出比例和析出物平均尺寸无影响。通过适当增加吹氩时间到5min,加钒球或五氧化二钒合金化就可达到与加钒铁合金化一样的钢水洁净度,钢筋伸长率可得到保证。

Strengthening mechanism of steels treated by barium-bearing alloys

The deoxidation, desulfurization, dephosphorization, microstructure, and mechanical properties of steels treated by barium-bearing alloys were investigated in laboratory and by industrial tests. The results show that barium takes part in the deoxidation reaction at the beginning of the experiments, generating oxide and sulfide compound inclusions, which easily float up from the molten steel, leading to the rapid reduction of total oxygen content to a very low level. The desulfurization and dephosphorization capabilities of calcium-bearing alloys increase with the addition of barium. The results of OM and SEM observations and mechanical property tests show that the structure of the steel treated by barium-bearing alloys is refined remarkably, the lamellar thickness of pearlitic structure decreases, and the pearlitic morphology shows clustering distribution. Less barium exists in steel substrate and the enrichment of barium-bearing precipitated phase mostly occurs in grain boundary and phase boundary, which can prevent the movement of grain boundary and dislocation during the heat treatment and the deformation processes. Therefore, the strength and toughness of barium-treated steels are improved by the effect of grain-boundary strengthening and nail-prick dislocation.

RE-Ca-Ti复合处理对ZG55钢组织与性能的影响

研究了RE－Ca及RE－Ca－Ti两种复合变质处理方法对改善ZG55钢组织与性能的影响。结果表明，加入适量的RE、Ca及Ti，可使钢的铸态一次晶细化．魏氏组织消除．铁素体由条状大块分布变为均匀的小块分布；非金属夹杂由不规则大块状聚集分布变为点状弥散分布。从而使钢具有较高的机械性能并克服了原钢种的热裂倾向大的缺点。此外，研究还表明，采用RE－Ca－Ti处理比RE－Ca处理效果好，但两者差值并不大，因此，一般情况下，只采用RE－Ca处理即可。

Microstructural Evolution of Co_(35)Cr_(25)Fe_(30)Ni_(10) TRIP Complex Concentrated Alloy with the Addition of Minor Cu and Its Effect on Mechanical Properties

The influences of minor Cu addition(2 and 4 at.%)on the microstructural evolution and room-temperature mechanical property of metastable Co_(35)Cr_(25)Fe_(30)Ni_(10)are systemically investigated in the present study.The results indicate that the thermally induced hexagonal close-packed(HCP)phase is absent when Cu was added,due to the increase in stacking fault energy(SFE).The 2%-Cu-added alloys showed the largest total elongation of 69%among the three alloys.With the addition of Cu content reaching 4 at.%,heterogeneous grain structures composed of coarse grains(~9μm)and fine grains(~4μm)and Cu-rich precipitates near the grain boundary are observed,showing the highest yield strength.Additionally,the segregation state of Cu was quantitatively characterized by electron probe microanalysis(EPMA).And effects of Cu addition on microstructures and tensile properties of(Co_(35)Cr_(25)Fe_(30)Ni_(10))_(100-x) Cu _(x) are also discussed.The findings are beneficial to comprehensively understand the Cu-containing complex concentrated alloys.

Preparation of ultrafine Ti (C, N)-based cermet using oxygen-rich powders

The availability using oxygen-rich powders to prepare ultrafine Ti(C,N)-based cermets was investigated. The deoxidation process, denitrification phenomenon and the effect of deoxidation on microstructure and mechanical properties of sintered samples were discussed, respectively. The results show that oxygen in the samples prepared even with high oxygen contained in starting powders can be almost completely cleaned away through suitable sintering process. The ultrafine oxygen-rich powders have a significant effect on microstructure, which promotes the formation of white core phase. A ultrafine Ti(C,N)-based cermet with mean particle size of 0. 30 μm, uniform microstructure and excellent mechanical properties is successfully prepared. It is also found that there exists severe denitrification phenomenon in the preparation process of ultrafine Ti(C,N)-based cermet.

淀粉-脂质/脂肪酸复合物研究进展

淀粉-脂质/脂肪酸复合物作为新型改性淀粉已成为国内外学者的研究热点,它是利用生物大分子之间的相互作用形成独特的复合体系实现对淀粉的改性,最终扩大了淀粉的应用范围。文中综述了淀粉-脂质/脂肪酸复合物的制备方法、影响因素、形成机理、微观结构和稳定性、对淀粉特性的影响及应用领域的研究进展,并对其存在的问题进行分析,以期为我国改性淀粉的发展提供新思路。

硼脱氧后的残留硼含量对纯铜组织及性能的影响

针对铜熔炼脱氧工艺,研究了采用硼粉脱氧后残留氧含量及残留硼含量对纯铜微观组织、力学性能和电学性能的影响。结果表明:随着硼加入量的增加,纯铜中氧含量快速降低,残留硼含量升高,纯铜微观组织中枝晶状的氧化亚铜相逐渐消失;随着残留硼含量从0×10^(-6)增加至8.8×10^(-6)时,纯铜的抗拉强度和硬度先升高后降低,伸长率不断升高,导电率升高;当残留硼含量为23×10^(-6)时,纯铜的抗拉强度为135.6 MPa,伸长率为55%,硬度为60.8 HV0.1,导电率为98.12%IACS。

复合变质与热处理对Al-18Si-4Cu-0.5Mg合金组织和性能的影响

采用室温拉伸实验、金相组织观察和扫描电镜观察研究了复合变质处理和T6热处理对过共晶Al-18Si-4Cu-0. 5Mg合金力学性能和显微组织的影响。结果表明,过共晶Al-18Si-4Cu-0.5Mg合金经P-RE-Sr复合变质处理后,初晶硅由粗大不规则板块状细化为细小片状,尺寸明显减小,共晶硅由细长针状转变为珊瑚状、短棒状和蠕虫状,经T6热处理后,初晶硅尺寸无明显变化,共晶硅发生熔断、球化;经P-RE-Sr复合变质处理后,抗拉强度由222MPa提高至236MPa,延伸率由3.22%提高至4.03%;复合变质合金经T6热处理后,抗拉强度大幅度提高,提高至320MPa,但延伸率略有下降,下降至3.37%。

复杂环境高强度耐蚀耐磨钢HNM450的开发及应用

研发了满足磨煤机复杂服役工况的高强度耐磨钢HNM450。其抗拉强度1727 MPa,断后伸长率14.5%,平均HBW硬度值522,-20℃冲击功38 J,具有良好的强度、塑性和低温韧性。模拟磨煤机实际服役工况的腐蚀磨损对比试验结果显示:HNM450产品200℃高温pH=5的弱酸性潮湿环境和200℃高温,pH=9的弱碱性潮湿环境下的耐腐蚀耐磨性能均明显优于HARDOX450钢。HNM450钢已经用于下游用户磨煤机的制造,实现了对进口耐磨钢HARDOX450的国产化替代。