Parameter optimization and mechanism of laser–arc hybrid welding of dissimilar Al alloy and stainless steel

Laser–cold metal transfer arc hybrid welding of 6061 Al alloy and AISI304 stainless steel (304SS) was carried out. Bead morphologies and intermetallic compound (IMC) layer characterizations of the joints were studied in detail. The optimal parameter range for accepted bead appearances (OPRBA) without surface and interface defects was obtained, and the growth mechanism of the IMC layer was summarized. The results showed that the nonuniformity in the thickness and shape along the fusion zone/304SS interface from the top surface to the bottom increases with increasing heat input and is more sensitive to laser power because the interface temperature is dominated by a high-temperature laser keyhole throughout the molten pool. As the welding parameters are within the OPRBA and the heat input is within the range of 80–110 J/mm, the joints are stronger than 130 MPa and the corresponding IMC layer thickness is at the range of 3–6.5 μm. The kinetic analysis showed that a controlling interface temperature no more than 1,120 °C may limit the growth of the IMC layer.     

Experimental and theoretical analysis of friction stir welding of Al–Cu joints

This paper presents a study of friction stir welding of aluminium and copper using experimental work and theoretical modelling. The 5083-H116 aluminium alloy and pure copper were successfully friction-stir-welded by offsetting the pin to the aluminium side and controlling the FSW parameters. A theoretical analysis is presented along with key findings. The process temperatures are predicted analytically using the inverse heat transfer method and correlated with experimental measurements. The temperature distribution in the immediate surroundings of the weld zone is investigated together with the microstructures and mechanical properties of the joint. This was supported by a finite element analysis using COMSOL Multiphysics. In this study, two rotational speeds were used and a range of offsets was applied to the pin. The microstructure analysis of the joints was undertaken. This revealed some particles of Cu inclusion in the nugget zone. The energy dispersive spectroscopy showed a higher diffusion rate of aluminium towards the interface while copper maintained a straight base line.     

Effect of strain amplitude and temperature on creep-fatigue behaviors of 9–12 % Cr steel

The creep-fatigue behaviors of P92 steel under strain range of 0.3 %–0.5 % and test temperature of 600–650 °C was studied carefully in this paper. With the increase of temperature, the creep-fatigue life is significantly reduced, and more vulnerable to temperature than strain amplitude. In addition, the dislocation density decreases with increasing creep fatigue, and the martensite laths become coarser. Furthermore, the increase of strain amplitude leads to more significant secondary cracks and fatigue striation. The higher temperature causes much deeper and larger dimples. During the test, the growth and accumulation of precipitates inevitably lead to stress concentration, resulting in material fracture and destruction. Finally, the linear cumulative damage (LCD), the modified ductility exhaustion (MDE) and the frequency separation life (FSL) model are used to predict the creep-fatigue life of P92 steel, and it is found that the frequency separation life model had the highest prediction accuracy among the threes.

     

Development of a MIAB welding module and experimental analysis of rotational behavior of arc—simulation of electromagnetic force distribution during MIAB welding of steel pipes using finite element analysis

Magnetically impelled arc butt (MIAB) welding is a unique forge welding process in which an arc is drawn in the gap between the two tubes to be welded in order to raise them to a high temperature to allow forging to form a solid-state weld. In this case, the arc is rotated with a high speed around the weld line by an electromagnetic force resulting from the interaction of the magnetic field and the arc current. This paper presents the details of the results and the conclusions of the experimental trials conducted on the MIAB module designed and developed based on the principle. Further, nonlinear electromagnetic analysis has been performed to determine the magnetic field and electromagnetic force distribution in MIAB process using finite element package ANSYS. Typical results of this analysis pertaining to magnetic field are compared with the experimental data for steel tubes (outer diameter 47 mm and thickness of 2 mm). It is observed that the results from finite element analysis and the experimental trials are in excellent agreement. The proposed three-dimensional finite element method model for electromagnetic force distribution facilitates comprehensive understanding of the arc rotation process in MIAB welding.     

Cavitation resistance of Cr–N coatings deposited on austenitic stainless steel at various temperatures

Cr–N coatings were deposited on austenitic stainless steel, X6CrNiTi18-10, by means of the cathodic arc evaporation method at three substrate temperatures: 200 °C, 350 °C and 500 °C. All coatings were found to have a composition of Cr(N), CrN and Cr₂N. The substrate temperature was found to have an influence on the hardness and Young's modulus of the Cr–N coatings. The investigation of nanocrystalline Cr–N coatings resistance to cavitation was performed in a cavitation tunnel with a slot cavitator and tap water as the medium. The estimated cavitation resistance parameters of the coatings were the incubation period of damage and total mass loss. It was found that the optimal coating cavitation resistance was deposited at 500 °C. The incubation period for the 500 °C deposition coating was the same as that of the uncoated X6CrNiTi18-10 steel, but the total mass loss was significantly lower than on the uncoated specimen. The scanning electron microscope analysis indicated that the damage process of the Cr–N coating mainly originates from the plastic deformation of the steel substrate–hard coating system, which appears by “micro-folding” of the surface. An increase of tensile stresses at the top of micro-folds initiates micro-cracks and delamination of Cr–N coating. The results of the investigation and the analysis indicate that the factors mainly responsible for cavitation resistance of the steel substrate/hard coating system are resistant to plastic deformation of the total system and coating adhesion.     

Fundamental investigation on nano-precision surface finishing of electroless Ni–P-plated STAVAX steel using magnetic compound fluid slurry

Electroless nickel–phosphorus (Ni–P) plating used in a range of hot embossing metal molds/dies and injection metal molds/dies must be manufactured to nano-precision roughness for proper operation of the molds/dies. We therefore developed a novel polishing technique for mirror surface finishing of this kind of magnetic material using a magnetic compound fluid (MCF) slurry. The effects of the magnetic and gravitational forces acting on the carbonyl iron particles (CIPs) and abrasive particles (APs) within the MCF slurry were studied first, and the behaviors of the CIPs and APs in the presence of an external magnetic field were predicted. Then, experiments were performed to confirm the predictions by investigating the distribution of the CIPs and APs on the working surface of the MCF slurry. Finally, four MCF slurries containing CIPs and APs with different diameters were employed to finish the Ni–P-plated STAVAX steel specimen at different working gaps. The results revealed that for the magnetic workpiece, the resultant vertical force attracted CIPs towards the work surface, whereas APs were pushed away from the work surface. However, the CIPs and APs showed opposite behaviors with the non-magnetic workpiece. The percentage of APs distributed on the working surface increased and the distribution became more even as either the diameter of the CIPs or the working gap increased, whereas that of CIPs had the opposite tendency. The MCF slurry containing bigger CIPs and smaller APs should be employed and the working gap should be set at a smaller value in order to perform mirror surface finishing of a magnetic Ni–P-plated surface. Under the experimental conditions in this work, the Ni–P-plated surface quality improved significantly, and a mirror surface roughness (Ra) of 4 nm was successfully achieved without leaving scratches or particle adhesion when using an MCF slurry containing CIPs 7 μm in diameter and APs 1 μm in diameter, showing that MCF slurries containing commercial CIPs are applicable to the nano-precision finishing of magnetic materials.     

Experimental investigation of surface quality for minimum quantity oil–water lubrication grinding

Effective lubrication and cooling is necessary to ensure grinding temperature levels not to become excessive during grinding process. Conventional grinding fluid has negative influences on the working environment in terms of the health of the machine operator. Furthermore, the using of grinding fluid is seen to increase production cost due to fluid purchase and disposal. One attractive alternative is the minimum quantity lubrication (MQL) grinding. In this study, oil–water was applied in the MQL grinding and the grinding results were compared with those of wet, dry, and pure oil MQL grinding. It is found that MQL grinding in comparison to dry grinding significantly enhances grinding performance in terms of improving the quality of the ground workpiece and reducing grinding temperature and forces. Compared with pure oil MQL grinding, the grinding temperature and the thickness of the affected layer for oil–water MQL grinding are lower. However, the tangential force and surface roughness for oil–water MQL grinding are higher than that for pure oil MQL grinding. This indicates that the former has a better cooling condition than the latter, but the lubrication capacity is contrary.     

Experimental studies of the cutting force and surface morphology of explosively clad Ti–steel plates

The present work pertains to the study of clad material such as titanium plated steel in drilling process. The study was conducted for two types of indexable insert drills with different configuration of the tool coatings (TiAlN/AlTiN + TiN and TiAlN/TiN), the same geometry of insert and fixed machining conditions. Drilling process was assessed by the analysis of thrust force, torque and signal fluctuations of PSD function. In this context, surface morphology of the drilled holes and contact area was analysed. It has been observed that the use of the PSD function allows assessment of the drilling process in different layers of clad materials. Also was found that the parameters of the surface morphology are dependent upon the type of layers of the clad and the type of drill. Furthermore the reduction in torque results in obtaining smaller values of surface roughness parameter especially in the area of volume parameters of the bearing area curve.     

G115Cr14Mo4V和8Cr4Mo4V淬回火工艺及性能研究

采用不同淬回火工艺对高温不锈轴承钢G115Cr14Mo4V和高温轴承钢8Cr4Mo4V进行热处理,观察两者的显微组织,检测淬火、回火后的硬度和残余奥氏体含量,并对高温硬度、冲击功和滚动接触疲劳寿命进行测试。结果表明：淬回火后G115Cr14Mo4V钢的室温硬度稍高于8Cr4Mo4V钢,两者的残余奥氏体含量都可控制在3%以内;在高温硬度和滚动接触疲劳额定寿命L10方面,G115Cr14Mo4V钢优于8Cr4Mo4V钢;在冲击功方面,8Cr4Mo4V钢优于G115Cr14Mo4V钢。     

Experimental analysis on mechanical interlocking of metal–polymer direct joining

Injection molded direct joining (IMDJ) is a method for direct joining of metals and polymers. In this work, we identified the most influential parameter for IMDJ and explained the reasons for successful joining by considering mechanical interlocking. We prepared hybrid joints of 30% glass-fiber-reinforced polybutylene terephthalate and aluminum alloy (A5052) plates with laser-treated surface dimples via IMDJ under various injection parameters. We studied the effects of the packing and holding pressures and the polymer temperatures on the joining strength. We discussed the reasons for the observed effects by considering mechanical interlocking, including the infiltration depth and the contact between the metal and the polymer. We found the packing pressure to be the most influential parameter. Moreover, the interaction between the packing pressure and the polymer temperature also influenced the joining strength considerably. The increased joining strength under various combinations of injection parameters was a result of deeper infiltration depth and better contact. We anticipate that the findings of this study will aid better selection of injection parameters for IMDJ.     

通用高速钢W9Mo3Cr4V

制造复杂刀具的材料,高速钢仍占主要地位,尤其在有色金属的切削加工中,还广泛使用高速钢刀具。长期以来,通用高速钢一直沿用W18Cr4V,属高钨系,简称W18。由于其一次碳化物不均匀度大,颗粒度粗,韧性较差,尤其是热塑性低,不能满足热轧各种成型工具的要求。六十年代以来,国际上已普遍使用钨钼系高速钢W6Mo5Cr4V2(简称M2)来代替W18高速钢,但M2钢脱碳严重,在我国现有锻轧     

通用高速钢W9Mo3Cr4V

制造复杂刀具的材料,高速钢仍占主要地位,尤其在有色金属的切削加工中,还广泛使用高速钢刀具。长期以来,通用高速钢一直沿用W18Cr4V,属高钨系,简称W18。由于其一次碳化物不均匀度大,颗粒度粗,韧性较差,尤其是热塑性低,不能满足热轧各种成型工具的要求。六十年代以来,国际上已普遍使用钨钼系高速钢W6Mo5Cr4V2(简称M2)来代替W18高速钢,但M2钢脱碳严重,在我国现有锻轧设备及退火设备落后的情况下,许多冶金厂不易解决脱碳严重的问题。此外,M2钢使用了较多的钼和钒,也不符合我国资源情况。     

CW6Mo5Cr4V2钢与W6Mo5Cr4V2钢的性能比较

比较了CW6Mo5Cr4V2钢与W6Mo5Cr4V2钢的性能。试验表明,在相同淬火温度下,CW6Mo5Cr4V2淬回火硬度和红硬性明显高于W6Mo5Cr4V2,淬火晶粒比W6Mo5Cr4V2粗,冲击功比W6Mo5Cr4V2低。CW6Mo5Cr4V2在1160-1200℃淬火可获得优良的综合机械性能。在1220℃以上淬火,CW6Mo5Cr4V2过热倾向显著,冲击功急剧下降。碳和钨钼含量的变化对CW6Mo5Cr4V2淬火温度的影响很大。要使CW6Mo5Cr4V2淬火易于控制,必须收窄CW6Mo5Cr4V2主要成分范围。CW6Mo5Cr4V2较适合于切削速度较高的刀具。     

Optimizing the geometric parameters of chamfered edge for rough machining Fe–Cr–Ni stainless steel

Geometry of cutting edge has great influence on performance and reliability of modern precision cutting tools. In this study, two-dimensional finite element model of orthogonal cutting of Fe–Cr–Ni stainless steel has been built to optimize the geometric parameters of chamfered edge. A method to measure the chip curl radius has been proposed. The effect of cutting edge geometric parameters on tool stress and chip curl radius has been analyzed. Then, the chamfered edge parameters have been optimized based on numerical simulation results. It finds that, keeping the equal material removal rate, the optimal geometric parameters of chamfered edge for rough machining Fe–Cr–Ni stainless steel are that the rake angle is from 16° to 17°, and the chamfer length is from 60 to 70 μm. Small (large) rake angle combined with small (large) chamfer length is more reasonable to reduce the tool stress. When the length of land is approximately equal to undeformed chip thickness and the rake angle is larger than 15°, the chip curl radius is minimal. The groove type with large radio of width to depth should be used in the chip breaking based on the optimization results.     

Cr4Mo4V钢制滚子的时效工艺

介绍了滚子的一般加工工艺和热处理工艺,对比在自然时效和人工时效下的磨削应力释放效果,优化人工时效工艺参数,有效保证了滚子的批直径变动量.     

Cr4Mo4V高温轴承钢的磨削试验

对Cr4Mo4V高温轴承钢制外圈沟道的磨削进行了试验,解决了生产中沟道表面质量问题,提高了零件的加工质量和精度,并提高了生产效率。