复合变质对过共晶铝硅合金晶体形貌的影响

采用光学显微镜等手段对复合变质处理后的过共晶铝硅合金显微组织、形貌进行了分析．结果表明：硅含量为20％和25％时,经过磷和稀土复合变质后,使粗大块状、条状的初晶硅的尺寸明显减小且棱角钝化,较大针状的共晶硅变为短杆状或颗粒状,使显微组织明显细化．而磷对含硅量30％的铝硅合金的初晶硅的细化效果不是很明显．     

原位Al2O3变质与热处理对铸造过共晶铝硅合金组织和性能的影响

利用金相显微镜(OM)、扫描电子显微镜(SEM)、X-射线能谱仪(EDS)、硬度计等测试手段,研究了在过共晶铝硅合金中加入CuO原位生成Al₂O₃对初晶硅的变质作用以及热处理对变质后的过共晶铝硅合金组织和性能的影响。结果表明：原位生成的Al₂O₃对过共晶铝硅合金的初晶硅的变质细化作用显著,同时生成的Al₂Cu型化合物作为增强相提高了过共晶铝硅合金的硬度。变质后的铝硅合金经过热处理后,针状的共晶硅球化,趋近于短棒状和球状,固溶8 h、时效8 h后合金硬度最大,可达维氏硬度HV 77.1,与热处理前相比,硬度增幅为1.3%。     

脉冲电压对过共晶Al-22％Si合金显微组织的影响

为改善过共晶Al—Si合金中硅相组织粗大对性能造成的不利影响,利用脉冲电场处理技术对液态合金进行细化处理。在脉冲频率为22Hz、作用时间为12S的情况下改变脉冲电压,分别取100V、200V和300V。研究结果表明：在脉冲频率和作用时间固定后,脉冲电压为200V时,合金细化效果最理想。合金中初晶硅及共晶硅组织均得到细化,尺寸减小,棱角圆整,多呈颗粒状或短杆状,同时合金的硬度也有所提高。     

硫化锌、锶复合变质对过共晶铝硅合金组织的影响

以Al-24Si合金为研究对象,通过添加不同含量的ZnS中间体和Al-Sr中间合金作为变质剂,利用金相显微镜(OM),X射线衍射仪(XRD)、能量分散谱仪(EDS)等分析手段研究了亚微米级ZnS、Sr复合变质对Al-24Si合金组织形貌的影响,结果表明:亚微米级ZnS与Sr复合变质能同时细化初晶硅和共晶硅,二者不会干扰各自的变质效果,可将初晶硅平均尺寸由120μm细化至30μm以下,共晶硅由针片状变质至短棒状或纤维状。     

过共晶Al-16%Si合金梯度功能材料的组织与性能

采用离心技术成功地制备了过共晶Al 1 6%Si合金梯度功能材料。采用金相及扫描电子显微镜、HV 5型小负荷维氏硬度计及销盘式ML 1 0 0型磨粒磨损试验机研究了该梯度功能材料的组织、硬度及耐磨性的分布规律。结果表明 ,由于Si的密度比Al液的密度稍低 ,在离心力场中初晶硅向试样内侧移动。Al 1 6%Si合金梯度功能材料的组织分布为 :最内层初晶硅含量最多、尺寸也最大 ,由内向外 ,初晶硅的体积分数及尺寸均逐渐减小 ,且呈梯度变化。在外层一定厚度内 ,完全不含初晶硅 ;硬度分布为内层硬度较高 ,由内向外硬度逐渐减小 ,呈梯度分布 ;耐磨性由内向外呈梯度下降趋势     

热处理工艺对电弧增材制造ZL114A铝合金耐蚀性能的影响

为了研究热处理工艺对电弧增材制造ZL114A铝合金耐蚀行为的影响,采用光学显微镜和附带能谱仪的扫描电子显微镜分析了第二相的形貌及成分,并采用电化学工作站测试了铝合金的腐蚀行为.结果表明：经过固溶和时效处理后,ZL114A铝合金的组织主要由α-(Al)基体、共晶Si和Mg₂Si相组成.当在540℃固溶处理时,随着固溶时间从2 h增加到14 h,合金中共晶硅相逐渐转变为球状.经过14 h的固溶处理后,合金表现出很强的钝化能力.合金经过时效处理后,随着时效时间从4 h增加到12 h,晶内析出的共晶硅和Mg₂Si相数量逐渐增多,合金耐蚀性能降低.     

稀土Ce对ZA27合金组织和力学性能的影响

在ZA27合金中加入稀土元素Ce,并采用挤压铸造的加工方法，寻求细化组织和提高力学性能的途径.稀土Ce使ZA27合金的晶粒细化，β相和ε相分布更均匀，并且在晶界处生成了不规则的化合物，该化合物包含Zn、Al、Cu、Ce、Mg等元素.随着含Ce量的增加，化合物的数量增多，有少量偏聚成大块.在挤压力作用下，晶界处ε相要少些.添加稀土Ce后，挤压铸造ZA27合金的抗拉强度、伸长率、硬度均有所提高.结果表明，含Ce量为0.15%时挤压铸造ZA27合金组织和力学性能最好.     

Zn、Y对普通凝固Mg-Zn-Y合金组织性能的影响

为了获得一种高质量的含有二十面体准晶相的准晶合金,采用金属型铸造方法制备了Mg-Zn-Y合金.利用扫描电子显微镜、能谱仪、X射线衍射仪和维氏硬度仪研究了Zn、Y元素对合金组织与性能的影响,并分析了准晶相的形成机制.结果表明,在普通凝固条件下准晶相可以直接在液相中形核并长大,合金硬度及准晶相的形貌、大小和分布与Zn、Y元素的含量密切相关.随着Zn含量的增加,Mg-x Zn-4.5Y合金硬度逐渐增大,组织中的准晶相由花瓣状向条状转变,且层片状共晶及α-Mg相逐渐消失.随着Y含量的增加,Mg-48Zn-y Y合金硬度逐渐增大,花瓣状准晶相数量逐渐增多,且层片状共晶组织变得更为致密.通过调节Zn、Y元素含量可以获得高质量准晶合金Mg-48Zn-13Y.     

变质与固溶处理对Al-Si-Cu系合金力学性能和微观组织的影响

通过金相观察,硬度和拉伸性能测试等手段,分析了固溶温度与变质剂Sr对Al Si10Cu1Mg0.4合金强韧性能与微观组织的影响。结果表明:随着固溶温度的提高,共晶硅经历熔断、球化和长大三个阶段并逐渐趋于均匀化;变质与未变质的铸态下的共晶硅的形貌和大小显著影响固溶温度对其熔断和球化效果;与未添加变质剂的合金相比,Sr变质的合金具有更细小的二次枝晶臂间距(secondary dendrite arm space,SDAS)和共晶硅,合金延伸率从未变质前平均的3.0%提高到4.4%,提高了46.7%,并且块状初晶硅明显减少。最终得到了最佳的固溶处理工艺为525℃×6 h,此工艺可以满足柴油机气缸盖发动机对各项机械性能的要求。     

轧制工艺对ZA35合金组织和性能的影响

为了提高ZA35合金的力学性能,采用轧制工艺制备ZA35合金板坯,利用x-射线衍射仪(XRD)、金相显微镜(OE)、扫描电子显微镜(SEM)以及能谱分析(EDS)等技术分析和检测了ZA35合金铸态、不同轧制态和热处理态的显微组织和性能.结果表明:轧制可以显著提高ZA35合金的综合力学性能,使抗拉强度提高了27.8%,硬度指标提高了36.4%,伸长率比铸态增加了近2倍.轧制使合金组织细化,初生α相增多,ε相由块状变成细小的点状弥散分布于枝晶间.轧制合金在经过365℃固溶3h和120℃时效12h热处理后合金力学性能最好,抗拉强度达到512MPa、伸长率为4.9%、硬度为HB127.     

SiC_p/ZA22复合材料高温力学性能

采用半固态挤压铸造工艺制备了SiC_p/ZA22复合材料,并测定了其高温条件下的抗拉强度、弹性模量及冲击韧性,同时,分析了复合材料高温性能提高的影响因素,并提出了优化的碳化硅颗粒尺寸和加入量.     

合金元素对钢基复合材料组织和性能的影响

研究了Si,Mn合金元素加入量对自生TiC颗粒增强的钢基复合材料的组织和性能的影响．结果表明,在自生TiC颗粒增强钢基复合材料中,随着Si,Mn合金化元素的升高,复合材料基体组织将经历从单相珠光体到珠光体马氏体,再到单相马氏体的变化过程．相应地,复合材料铸态硬度从单相珠光体的HRC43．1变化到单相马氏体的HRC55．Si,Mn合金化元素的含量对热处理态复合材料的硬度也有明显影响,但对冲击韧性影响不大。     

硅、稀土元素对 ZA27 力学性能影响规律的研究

采用正交组合回归设计试验方法，研究了硅、稀土元素对ＺＡ２７合金力学性能的影响规律。研究结果表明，硅、稀土元素对合金的抗压强度、冲击韧性产生显著影响，且对综合力学性能的影响存在最佳配比。     

Microstructure and mechanical properties of WC-20wt% Co/ZrO2（3Y）cermet composites

The cermet composites WC-20wt%Co/ZrO2（E6）with four different comtents of ZrO2（3Y）were prepared by normal vacuum sinter processing;the optical microscope and SEMwere used to characterize their microstructures.The hardness.bending strength and impact toughness of the specimens were determined.The experimental results show that ZrO2（3Y） particles in WC-20wt%Co matrix are sphcrical particles in different sizes which are distributed uniformly in Co phases and WC phases,the bending strength and impact toughness of the WC-20wt%Co cermet composites added ZrO2（3Y）improve remarkably.but the hardness values have little change.     

Fabrication and Microstructure Evolution of Niobium-Niobium Silicide Composites by Spark Plasma Sintering

By using Nb and Si elemental powders as raw materials,dense Nb/Nb 5 Si 3 composites were successfully fabricated by a spark plasma sintering(SPS)technology.The microstructure of the fabricated composites was analyzed by OM,SEM,XRD and EPMA;the microstructure evolution of the composites was also investigated by a quenching test.The experimental results show that the prepared composites consist of Nb and Nb 5 Si 3 phases;Nb particle uniformly distributes in the in-situ synthesized Nb5 Si3 matrix.During the SPS process,an interfacial reaction occurs between Nb and Si particles to synthesize Nb 5 Si 3 until reactant silicon has been completely depleted.     

Processing technique and sliding friction and wear behavior of TiB2／ZA27 composite

In-situ TiB2 particles reinforced ZA27 composite was prepared by the stir-casting technique and a twostep method. TiB2/Al composite was produced by incorporating K2 TiF6, KBF4 salts and other agents into Al melt. As a master alloy, TiB2/Al composite was used to manufacture TiB2/ZA27 composite, which results in the generation of well-distributed reinforcing TiB2 phase. The hardness, friction and wear behavior of TiB2/ZA27 composite were investigated. The results show that the hardness of the composite is enhanced with increasing the content of TiB2 particles, the incorporation of TiB2 reduces the wear rate of TiB2/ZA27 composite and improves the friction property under lubricated and dry sliding friction conditions. The worn track width of ZA27 alloy is 1.6 and 2.5 times as long as that of 2.1%TiB2/ZA27 composite at 150 N and 700 N load under lubricated conditions, which indicates that TiB2/ZA27 composite possesses higher bearing ability.     

Effect of Nano-sized B_4C Addition on the Mechanical Properties of ZA27 Composites

In order to understand the influence of nano-sized B_4C additive on ZA27 alloy, mechanical and physical properties of ZA27-B_4C nanocomposites were investigated in terms of B_4C content. While physical properties were determined in terms of microstructural studies, density and porosity tests, mechanical properties were determined in terms of ultimate tensile strength(UTS) and hardness experiments. Morphological and microstructural studies were carried out with scanning electron microscopy(SEM). The experimental results indicate that nano-sized B_4C can be used to enhance the mechanical properties of ZA27 alloy effectively. The highest mechanical performance can be obtained at ZA27-0.5% B_4C(in weight) nanocomposite with values of tensile strength(247 MPa) and hardness(141,18 BH) and low partial porosity(0.5%). After a pick point, increasing B_4C ratio may cause the formation of agglomeration in grain boundaries, that's why density, tensile strength, and hardness values are declined.     

As-cast microstructure,mechanical properties and casting fluidity of ZA84 magnesium alloy containing TiC

The as-cast microstructure, mechanical properties and casting fluidity of ZA84 alloy containing TiC were investigated. The experimental results indicate that adding 0.5wt%TiC to ZA84 alloy can refine the as-cast microstructure, and do not cause the formation of any new phase. After 0.5wt%TiC was added to the ZA84 alloy, the morphology of ternary phases on the grain boundaries changed from coarse quasi-continuous net to fine disconnected net, and the distribution of ternary phases became dispersive and homogeneous. At the same time, the tensile properties of ZA84＋0.5TiC alloy at room temperature were comparable to those of AZ91D alloy, and were higher than those of ZA84 alloy. At 150 ℃, the tensile and creep properties of ZA84＋0.5TiC alloy were also higher than those of ZA84 and AZ91D alloys. In addition, compared with the AZ91D alloy, the casting fluidity of ZA84＋0.5TiC alloy was slightly poor, but better than that of ZA84 alloy. The reason could be related to the effect of TiC on the solidification temperature range of ZA84 alloy.     

Effect of TiO2 addition on zirconia-mullite composites fabricated by in-situ controlled crystallization of Si-Al-Zr-O amorphous bulk

Zirconia-mullite composite ceramics were fabricated by in-situ controlled crystallization of Si-Al-Zr-O amorphous bulk.The effects of TiO2 addition on the fabrication of zirconia-mullite composites were investigated.The ultra-fine zirconia-mullite composite ceramics were prepared from the amorphous bulk treated at 980 °C for nucleation and 1 140 °C for crystallization.The phase transformation of the ceramics was examined using differential scanning calorimetry (DSC) and X-ray diffractometry (XRD).The micros...     

Microstructure and mechanical properties of high-Cr cast iron bars reinforced Hadfield steel matrix composites

To obtain the compatible material of high hardness and high toughness, Hadfield steel matrix composites, reinforced by high-Cr cast iron bars made of flux-cored welding wires, which were inserted into the Hadfield steel melt, were investigated. The mechanical properties of three materials, i e, composites for as-cast and quenching-water condition, as well as Hadfield steel, were compared. The results show that the alloy powder inside flux-cored welding wires can be melted by the heat capacity of Hadfield steel melt and solidify into high-Cr cast iron bars. The impact toughness of the composite for quenching-water condition is higher than that of the composite for as-cast condition and is lower than that of the Hadfield steel, but it can still meet the requirements of hardness and toughness in industrial application. Regardless of load variation, composite for quenching-water condition shows better wear resistance than those of the composite for as-cast condition and Hadfield steel. The modified fracture toughness and wear resistance of composites are attributed to not only the combining actions of Hadfield steel matrix and high-Cr cast iron bars, but also the effect of heat treatment.