热处理对GH4169激光焊接头组织性能的影响

针对2 mm厚的GH4169镍基合金板材进行激光对焊,研究热处理对GH4169激光焊接头组织和性能的影响。采用线切割方法制备激光焊接头试样,对热处理和非热处理激光焊接头进行拉伸实验、硬度测定、OM分析、SEM分析、EDS分析和XRD相分析。实验结果表明:热处理后接头抗拉强度为1372 MPa,延伸率为14%,焊缝平均硬度为473HV;较未热处理接头强度提高52%,延伸率降低71%,硬度提高69%。OM、SEM、EDS和XRD分析表明:对GH4169激光焊接头热处理能细化焊缝晶粒,改善枝晶形态,消除残余应力,析出δ相、γ′相和γ″相,使得焊接接头硬度和强度有所提高。     

激光照射原位生成SiC晶须时粘结剂对晶须的影响

进行了含粘结剂和不含粘结剂的SiC纳米颗粒激光照射原位生成SiC晶须的比对试验,用X射线衍射仪(XRD)和扫描电子显微镜(SEM)分析了晶须的相组成和微观形貌,研究了粘结剂对生成晶须的影响。结果表明,在适当的激光参数下,不含粘结剂和含粘结剂的样品中均有晶须生成,不含粘结剂样品中晶须数量较少,而含粘结剂样品中晶须数量众多,且尺寸、形态各异。SiC纳米颗粒中掺入粘结剂可大幅度提高SiC晶须的生成数量,但并不影响晶须的纯度。     

Effect of SiC nanoparticles on the mechanical properties of steel-based nanocomposite produced by accumulative roll bonding process

In the present work, the effect of SiC nanoparticles on the mechanical properties of steel-based nanocomposite produced by accumulative roll bonding (ARB) process was investigated. The microstructure of the fabricated nanocomposites after fourth ARB cycle was exhibited an excellent distribution of SiC nanoparticles in the interstitial free (IF) steel matrix without any porosity. The findings revealed that with increasing the number of ARB cycles, the tensile strength of the ARB-processed pure IF steel and also nanocomposites was improved, but their elongation was decreased at first step and then was increased at second step. The tensile strength of the ARB-processed pure IF steel and nanocomposites was 4.5 and 6 times higher than the same value was obtained for annealed IF steel, respectively. In addition, the ARB-processed pure IF steel and nanocomposite was exhibited a higher hardness than the annealed IF steel so that the hardness values of the pure IF steel and nanocomposite were 3.78 and 4.44 times higher than that of the annealed IF steel.     

Experimental Investigation and Optimization of Process Parameters of Al/SiC MMCs Finished by Abrasive Flow Machining

In the era of nontraditional finishing processes, it is of upmost importance that these processes can be applied to composite materials as these have replaced traditional materials in many applications. Abrasive Flow Machining (AFM) is an advanced finishing process. Composite materials have replaced traditional materials as their properties such as light weight, high strength, and good economy are of great benefit. In the literature, work has been reported on AFM of materials such as aluminum, brass, and EN8. In the present work, composite materials with a high percentage of SiC (e.g., 20–60% SiC in Al/SiC composites) were machined using abrasive flow finishing. The Taguchi method was applied to find the effect of input parameters on material removal rate (MRR), change in surface roughness (ΔR_a), and surface topography, and L27 array was designed for experimentation. It was observed that extrusion pressure is the most significant factor in regard to MRR and ΔR_a. Optimization of response parameters (MRR and ΔR_a) was determined using the Taguchi method. Microstructure analysis was also done for workpiece materials using SEM and XRD.     

Effect of SiC content and orientation on the properties of Si/SiC ceramic composite

Silicon/silicon carbide ceramic composites are made by infiltrating carbonaceous material with liquid silicon to form SiC crystallites dispersed in a silicon matrix. The present study was conducted to determine the effects on the room temperature properties of density, elastic modulus, strength, and fracture toughness by varying the amount and distribution of the SiC crystallites. Most of the work involved uniaxially aligned SiC crystals of varying volume fraction tested both longitudinally and transversely to the converted fibre axis.     

基于SLS/CIP工艺SiC陶瓷的制备及其性能

以喷雾干燥的SiC-Al_2O_3-Y_2O_3造粒粉为原料,使用机械混合法得到复合粉体,通过激光选区烧结/冷等静压技术并结合液相烧结工艺制备出SiC陶瓷,对SiC陶瓷的物相组成、显微结构、抗弯强度及密度进行表征。结果表明:喷雾造粒粉平均粒径为39.43μm,球形度较高,流动性良好,适用于SLS成型;SLS成型最优参数为激光功率7W、扫描间距0.15mm、扫描速率2200mm/s、单层层厚0.15mm且CIP压力为80MPa时, SiC陶瓷素坯的性能最佳,抗弯强度为(2.23±0.10)MPa,密度为(1.31±0.05)g/cm^3;在1950℃下烧结2h后,样品发生了致密化,SiC陶瓷密度为(1.95±0.17)g/cm^3,相对密度为(60.81±5.31)%,抗弯强度为(55.43±4.04)MPa。     

Ni中间层对QBe2.5/钢激光点焊接头力学性能的影响

流量阀的执行机构常应用铍青铜/钢复合元件,本文采用0.05 mm纯Ni作为中间层对QBe2.5铍青铜薄片与20#钢异种金属激光点焊搭接接头力学性能进行优化.通过光学显微镜、拉剪试验、显微硬度计和能谱测试仪对比分析添加Ni与不添加Ni层时焊接接头的成形、力学性能以及元素分布.研究表明:与未加镍层接头相比,加镍中间层的焊缝熔深较小,且基本不出现下塌现象,加镍中间层比未加中间层的接头抗拉剪力提高了61.5%;加入镍中间层后的焊缝中Fe元素含量增加,而Cu元素含量降低,接头韧性提高;加镍中间层的接头焊缝硬度值沿焊点深度方向逐渐增大,而未加镍层的基本不变,且加镍层比未加镍层的接头界面显微硬度值低.镍中间层材料可以显著改善铍青铜/钢异种金属接头焊缝熔合比,提高接头的抗拉剪强度、塑性和韧性     

Hot formability studies on 359/SiC/20p and their application in forging optimisation

Hot formability of 359/SiC/20p was investigated in temperature and strain rate ranges from 375 to 500°C and from 0.003 to 10 s^-1, respectively. Flow stress and ductility were studied as a function of deforming conditions. A microstructural damage analysis showed that, at higher strain rates and lower temperatures, stress concentrations at the matrix-particle interfaces strongly affect the cavitation process: stresses become large enough that the interface can separate or particles can crack. Conversely, when temperature increases and strain rate decreases, diffusional processes and grain boundary sliding become the preferential mechanisms for void nucleation and growth. A damage criterion is proposed, based on both FEM simulations and ductility data. The criterion results in very good agreement with the experimental damage measurements performed on an H-section component forged under similar conditions. The criterion was used in the optimisation of forging conditions.     

先驱体浸渍-裂解SiC界面改性涂层对气相渗硅3D-C_f/SiC复合材料力学性能的影响

界面改性涂层对调节复合材料的力学性能起到重要作用。特别是在气相渗硅(GSI)制备C_f/SiC复合材料时,合适的界面改性涂层一方面保护C纤维不受Si反应侵蚀,另一方面调节C纤维和SiC基体的界面结合状况。通过在3D-C纤维预制件中制备先驱体浸渍-裂解(PIP)SiC涂层来进行界面改性,研究了PIP-SiC涂层对GSI C_f/SiC复合材料力学性能的影响。结果表明:无涂层改性的GSI C_f/SiC复合材料力学性能较差,呈现脆性断裂特征,其弯曲强度、弯曲模量和断裂韧性分别为87.6 MPa、56.9GPa和2.1 MPa·m~(1/2)。具有PIP-SiC界面改性涂层的C_f/SiC复合材料力学性能得到改善,PIP-SiC涂层改性后,GSI C_f/SiC复合材料的弯曲强度、弯曲模量和断裂韧性随着PIP-SiC周期数的增加而降低,PIP-SiC为1个周期制备的GSI C_f/SiC复合材料的力学性能最高,其弯曲强度、弯曲模量、断裂韧性分别为185.2 MPa、91.1GPa和5.5 MPa·m~(1/2)。PIP-SiC界面改性涂层的作用机制主要体现在载荷传递和"阻挡"Si的侵蚀2个方面。     

Effect of melt,solidification and heat-treatment processing parameters on the properties of Al-Si-Mg/SiC(p) composites

With the recent renovations in casting technology and foundry procedures, Al-Si-Mg alloys reinforced with SiC particulates are being increasingly employed in automotive and aerospace applications. The SiC reinforcement particles influence the solidification process in various ways, affecting the fluidity and castability of these composites.This articles reviews the results of an extensive study carried out on different aspects of Al-Si-Mg/SiC_(p)-type metal-matrix composites containing 7 or 10 wt% Si, reinforced with either 10 or 20 vol% SiC particulates. Aspects investigated include the castability and soundness in terms of melt fluidity, the effect of the solidification rate and of inclusions on the mechanical properties, and optimization of the heat-treatment parameters with regard to these properties. The influence of the processing parameters on the mechanical properties was determined by monitoring the microstructural changes taking place during the various stages of processing, by measurements of the dendrite arm spacing, porosity and SiC-particle content and distribution in the castings obtained, as well as the amount of oxide inclusions and other harmful reaction products such as Al₄C₃ present therein. The effect of employing the fluxing procedure commonly used in Al-Si-Mg alloys on the mechanical properties of one of the four composites studied is also reported.     

激光照射SiC纳米颗粒原位生成SiC晶须

以激光为热源,以SiC纳米颗粒材料为前驱体,用激光照射SiC纳米颗粒原位生长晶须.结果表明:由于激光能量输出的瞬时特性,SiC纳米颗粒受到激光的照射可瞬时生成SiC晶须.随着激光功率的提高,晶须的直径从纳米级增大到微米级.由于在激光光斑内能量呈高斯分布,光斑内不同区域的SiC颗粒的温度不同,致使生成的晶须形态在不同的区域分别呈现为团絮状、网状和棒状等.X射线衍射分析表明,激光照射SiC纳米颗粒原位生长的晶须具有很高的纯度.     

TWIP钢激光拼焊板的力学性能及微观组织分析

为评价TWIP钢的焊接性能,对1.2 mm厚的Fe-Mn-C系TWIP钢进行了激光拼焊实验,用线扫描分析了锰元素的分布,对拼焊板进行了拉伸试验,用扫描电镜观察了拉伸断口形貌,采用背散射电子分析技术分析了拉伸前后的组织变化及孪晶形成,测试了维氏硬度的分布曲线.实验结果表明:焊缝区未发生Mn元素的挥发,室温下为显著的柱状枝晶铸态组织;断裂发生在存在气孔等微小缺陷的焊缝区,拼焊板强度与母材接近,韧性显著降低;拉伸过程中有大量的形变孪晶形成,拉伸前后均为全奥氏体组织.     

Effect of welding parameters on microstructure and mechanical properties of friction stir spot welded 5052 aluminum alloy

Friction stir spot welding (FSSW) is a newly-developed solid state joining technology. In this study, two types of FSSW, normal FSSW and walking FSSW, are applied to join the 5052-H112 aluminum alloy sheets with 1 mm thickness and then the effect of the rotational speed and dwell time on microstructure and mechanical properties is discussed. The lower sheet material underneath the hook didn’t flow into the upper sheet due to the concave surface in the shoulder and groove in the anvil. The hardness profile of the welds exhibited a W-shaped appearance and the minimum hardness was measured in the HAZ. The results of tensile/shear tests and cross-tension tests indicate that the joint strength decreases with increasing rotational speed, while it’s not affected significantly by dwell time. At the rotational speed of 1541 rpm, the tensile/shear strength and cross-tension strength reached the maximum of 2847.7 N and 902.1 N corresponding to the dwell time of 5 s and 15 s. Two different fracture modes were observed under both tensile/shear and cross-tension loadings: shear fracture and tensile/shear mixed fracture under tensile/shear loadings, and nugget debonding and pull-out under cross-tension loadings. The performance of the welds plays a predominant role in determining the type of fracture modes. In addition, the adoption of walking FSSW brings unremarkable improvements in weld strength.     

焊接参数对铁素体不锈钢搅拌摩擦焊接头组织及性能的影响

对4mm厚T4003铁素体不锈钢进行搅拌摩擦焊接工艺实验,研究焊接参数对接头组织特征、硬度分布及常温和低温冲击韧性的影响。结果表明:接头搅拌区和热力影响区由铁素体和马氏体双相组织构成;接头搅拌区组织沿试样厚度方向存在非均质性,且随转速的降低及焊接速率的增加越发显著;转速从150r/min增加至250r/min,前进侧热力影响区组织呈现小梯度过渡趋势,无明显变形拉长特征。焊缝硬度分布相对均匀,其最高硬度为290HV,约为母材的1.87倍。焊接参数和温度对接头的冲击吸收功有较大影响:常温(20℃)下,热影响区为母材的90%～92%,搅拌区为母材的85%～103%;低温(-20℃)下,热影响区为母材的87%～97%,搅拌区为母材的82%～95%,表明焊缝区仍具有较好强韧匹配。     

Effects of SiC,Al2O3, and ZrO2 particles on the LBMed characteristics of Al/SiC,Al/Al2O3, and Al/ZrO2 MMCs prepared by stir casting process

The effects of SiC, Al₂O₃, and ZrO₂ particles on the characteristics of Al/SiC, Al/Al₂O₃, and Al/ZrO₂ metal matrix composites (MMCs) have been studied in the present research work. The comparison of machining characteristics has been done to analyze the behavior of various reinforced particles with the variation of laser machining variables. The output characteristics such as dross height and kerf deviation have been investigated and compared with each MMCs. SEM and XRD have been used for the investigation of morphological changes in the structure and agglomeration of reinforced particles. The crack and recast layer formation has been examined in the specimens of higher quantity of reinforced particles. It was observed that the MMC material reinforced with SiC particles has shown different behavior as compared to other MMC materials.     

Investigating effects of process parameters on microstructural and mechanical properties of Al5052/SiC metal matrix composite fabricated via friction stir processing

Friction stir processing (FSP) is a novel process for refinement of microstructure, improvement of material’s mechanical properties and production of surface layer composites. In this investigation via friction stir processing, metal matrix composite (MMC) was fabricated on surface of 5052 aluminum sheets by means of 5 μm and 50 nm SiC particles. Influence of tool rotational speed, traverse speed, number of FSP passes, shift of rotational direction between passes and particle size was studied on distribution of SiC particles in metal matrix, microstructure, microhardness and wear properties of specimens. Optimum of tool rotational and traverse speed for achieving desired powder dispersion in MMC was found. Results show that change of tool rotational direction between FSP passes, increase in number of passes and decrease of SiC particles size enhance hardness and wear properties.     

Effect of welding parameters on microstructure and mechanical properties of friction stir welded 2219Al-T6 joints

The effect of friction stir welding (FSW) parameters on the microstructure and mechanical properties of 5.6 mm thick 2219Al-T6 joints was investigated in detail. While the sound FSW joints could be obtained under lower rotation rates of 400–800 rpm and welding speeds of 100–800 mm/min; higher rotation rates of 1200–1600 rpm easily led to the tunnel and void defects. The FSW thermal cycle resulted in low hardness zones (LHZs) on both retreating side (RS) and advancing side (AS). The LHZs may be located at the interface between the nugget zone (NZ) and the thermo-mechanically affected zone (TMAZ), at the TMAZ, or at the heat affected zone under the varied welding parameters. The tensile strength of FSW 2219Al-T6 joints increased when increasing the welding speed from 100 to 800 mm/min, and was weakly dependent on the rotation rates from 400 to 1200 rpm. The FSW 2219Al-T6 joints fractured along the LHZ on the RS.