Thermal analysis of functionally graded coating AlSi alloy and steel pistons

Functionally graded coatings are coating systems used to increase performances of high temperature components in diesel engines. These coatings consist of a transition from the metallic bond layer to cermet and from cermet to the ceramic layer. In this study, thermal behavior of functional graded coatings on AlSi and steel piston materials was investigated by means of using a commercial code, namely ANSYS. Thermal analyses were employed to deposit metallic, cermet and ceramic powders such as NiCrAl, NiCrAl + MgZrO₃ and MgZrO₃ on the substrate. The numerical results of AlSi and steel pistons are compared with each other. It was shown that the maximum surface temperature of the functional graded coating AlSi alloy and steel pistons was increased by 28% and 17%, respectively.     

Aluminum alloy pistons reinforced with SiC fabricated by centrifugal casting

Hypereutectic Al-Si alloy-based composite pistons reinforced with SiC particles locally at the head were fabricated by centrifugal casting. The effects of various technique parameters, i.e., the slurry temperature of the alloy, the mold temperature and the rotation speed of the mold, on the particle segregation were investigated, and the macromorphologies and microstructures of pistons were observed. The mechanical properties, such as hardness and wear resistance along the axis of the piston and the thermal expansion coefficient at the piston head, were measured. The results showed that, (1) centrifugal casting can be used as a new and effective method in manufacturing pistons, and reasonable parameters were 850 °C, 600 °C and 800 rpm for the slurry temperature of the alloy, the mold temperature and the rotation speed of the mold, respectively; (2) the hardness values of pistons fabricated by centrifugal casting gradually increased from the piston skirt to the piston head, and the average hardness value in piston heads was improved by 23.7HRB over that of pistons fabricated by gravity permanent mold casting; (3) the piston heads showed excellent wear resistance, and the wear rate of piston heads decreased by 70.3% over that of the piston fabricated by gravity permanent mold casting; and (4) the average linear expansion coefficient of the piston head was 15.3 × 10⁻⁶ K⁻¹ and decreased by 23.1% over that of pistons fabricated by gravity permanent mold casting.     

EN AW-4032 T6 Piston Alloy After High-Temperature Exposure: Residual Strength and Microstructural Features

This study aims to evaluate the effects of prolonged thermal exposure on both microstructural evolution and mechanical properties of the EN AW-4032 T6 piston alloy. For the purpose, the experimental activities have been carried out on samples machined from forged and heat-treated automotive pistons. The effects of overaging have been investigated in the temperature range of 140-290 °C, firstly by evaluating the time-temperature-hardness curves and then by carrying out room-temperature tensile tests on overaged samples. The material softening was substantial and extremely rapid when the soaking temperature exceeded 250 °C. During overaging, both the tensile strength and the residual hardness considerably decreased, and a relationship between these parameters has been established. The alloy behavior in the plastic field has been modeled according to the Hollomon’s equation, showing that both the strain hardening exponent and the strength coefficient are a function of the residual hardness. The results were finally related to the corresponding microstructural changes: OM and FEG-SEM metallographic and fractographic analyses on overaged samples gave evidence of coarsened precipitates along the grain boundaries.     

Thermal analysis and microscopic characterization of the piston alloy AlSi13Cu4Ni2Mg

In this research paper, the phases identified by thermal and microscopic analysis of the piston alloy AlSi13Cu4Ni2Mg, which was solidified under different conditions, are presented and compared with different piston alloys. Piston alloys are a group of casting Al–Si alloys, well-known as wear resistant materials, which are widely used as the piston materials for internal combustion engines because of their low thermal expansion coefficient and high wear resistance when alloyed with other elements such as copper, magnesium and nickel. Depending on the combination of alloying elements and other impacting factors, pistons alloys with different mechanical and physical properties are obtained.     

38MnVS非调质钢活塞锻后控制冷却工艺

对38MnVS非调质钢活塞进行锻后冷却处理并探讨了不同冷却工艺对非调质钢活塞的影响规律.首先,分析了不同冷却速率对非调质钢活塞的组织性能和力学性能的影响,可知,在冷却速率为50～90℃·min-1下,非调质钢析出珠光体及铁素体时各方面的性能最优.然后,利用分选装置对非调质钢活塞锻件进行预选,挑选出达到合格锻造温度的活塞...     

Characterization of black rust staining of unpassivated 55% Al–Zn alloy coatings. Effect of temperature, pH and wet storage

Wet storage staining is a phenomenon that occurs on both zinc coated and 55% Al–Zn coated steel sheets during shipment or storage in damp conditions. Whereas zinc coated sheets form white corrosion products, 55% Al–Zn coated steel sheets form black corrosion products. The effect of temperature, pH and wet storage on the occurrence of black rust staining of unpassivated Aluzink samples has been investigated in the laboratory in terms of corrosion product formation and composition. A characterization of corrosion products formed has been performed mainly based on scanning electron microscopy with X-ray microanalyses (SEM/EDS) for morphological and quantitative analyses and X-ray diffraction techniques (XRD) for crystalline phase identification. Black rust formation is strongly related to alkaline pH regions and is enhanced by the temperature. All black panels show the presence of Bayerite (Al(OH)₃), mainly formed on the aluminum rich dendrite branches and a basic zinc aluminum carbonate (Zn₆Al₂(OH)₁₆CO₃·4H₂O) formed in the zinc rich interdendritic alloy regions in contact with air. Blackening of Aluzink surfaces is connected to differences in optical properties of embedded metallic zinc and/or aluminum particles of different shape and size in the corrosion layer.     

The examination of corrosion behaviors of hap coated Ti implant materials and 316L SS by sol-gel method

In this research, hydroxyapatite (HAP) coatings have been produced on Ti, Ti6Al4V alloy and 316L stainless steel substrates by sol-gel method. (NH₄) · H₂PO₄ is taken as P precursor and Ca(NO₃)₂ · 4H₂O is taken as Ca precursor to obtain HAP coating. Additionally, three different pretreatment processes (HNO₃, anodic polarization, base-acide (BA)) have been applied to Ti, Ti6Al4V alloy and 316L stainless steel substrates. The corrosion behaviors of bare and HAP coated samples are examined in Ringer and 0.9% NaCl. HAP coated Ti have showed over 87.85% inhibition. HAP coated Ti6Al4V alloys have showed over 87.33% inhibition. In Ringer solution, 99.24% inhibition has been showed in HAP coated anodic pretreatment for 316L stainless steel. All pretreatment processes are effective on clinging of HAP coating to the surface. It is seen that impedance values have increased in HAP coatings (Ti and Ti6Al4V). HAP coatings have raised the corrosion resistance of Ti and Ti6Al4V. The values of polarization resistance in HAP coated samples have increased for 316L stainless steel in 0.9% NaCl and Ringer solutions. It is seen in SEM images that open pores and attachments among pores have been observed in the coating, which increases osteointegration. It is noted in EDX analyses of the surfaces of the HAP coated samples that there is only Ca, O, and P on the surface. Ca/P ratio varies in 1.84–2.00 ranges. As Ca/P ratio increases, the inhibition increases too. It is seen in XRD images of HAP powder that there are HA ate structures. Additionally, it is seen in FTIR analysis, characteristic HA absorption bands have occurred in sintered powders.     

Enhancement of mechanical and wear properties of tungsten carbide coated AA 6063 alloy using detonation gun technique

Aluminium 6063 alloy as substrate was coated with WC-12% Co using the detonation spray gun technique. The coated specimen showed 5.6x increase in hardness over the uncoated substrate. Wear analysis was conducted on the coated specimen based on Taguchi’s L₂₇ orthogonal by taking load (10, 20, 30?N), sliding velocity (1, 2, 3?m?s^?1) and sliding distance (750, 1250, 1750?m) as parameters. Wear rate was observed to increase with an increase in load and sliding velocity, whereas initial increase and a subsequent decrease in wear rate was observed with an increase in sliding distance. Analysis of variance predicted that load has a higher influence on the loss of material. Load and sliding distance interaction showed a high influence over loss of material than any other individual parameter’s influence. SEM and XRD analysis was conducted over worn surfaces to help elucidate the wear mechanism. The results from the present work may find application in piston rings and cylinder liners.     

Corrosion behaviour of single and double layer hydroxyapatite coatings on 316L stainless steel by plasma spray

AISI316L stainless steel is extensively used in orthopedic and dental applications. However, this alloy exhibits low integration behaviour when it comes in contact with surrounding bone tissue and implant healing duration can be as much as few months. The aim of this study is the fabrication of biocompatible hydroxyapatite (HA) coatings on stainless steel substrate in order to accelerate the process of osseointegration of implants. The biocompatible single layer of Titania (TiO₂), Hydroxyapatite and bi-layer TiO₂/HA coatings were deposited by atmospheric plasma spray on 316L stainless steel. Coated and uncoated stainless steel specimens were incubated in simulated body fluids and 0.9% NaCl solutions for 1h and 7 days. In vitro electrochemical-corrosion evaluation of coated and uncoated stainless steel specimens have been investigated by Tafel extrapolation and linear polarization methods. Results indicates that corrosion resistance of single layer HA coated stainless steel specimens are superior to single layer TiO₂ and bi-layer HA/TiO₂ coated stainless steel specimens.     

Effect of fluxing chemical: An option for Zn-5wt.%Al alloy coating on wire surface by single hot dip process

The corrosion of wire is one of the primary causes for premature failure. The ideal way to overcome this problem is to provide corrosion protection right at the time of manufacturing. It is well established fact that Zn-5 wt.% Al alloy coating on steel surface provides much better protection against corrosion than the conventional pure Zn coating. Conventional fluxing operation is done on wire surface using zinc and ammonium chloride mixture before dipping in molten zinc bath. Galvanization bath temperature of about 415 °C for Zn-5 wt.% Al alloy coating on wire surface develops black spots of AlCl₃ when conventional flux is used. Double dip process is being followed for Zn alloy coating on wire surface due to non availability of suitable flux. An effort has been made to develop a suitable flux to obtain Zn-5 wt.% Al alloy coating on wire surface by single hot dip process. A salt mixture (containing zinc, ammonium, sodium, potassium, cobalt and lead chloride) was formulated based on the decomposition temperature of individual chloride salts. Differential thermal and thermo gravimetric analysis indicate the temperatures for complete decomposition of conventional and formulated flux are 445 and 410 °C, respectively. The lower decomposition temperature of formulated flux is ensured black spot free Zn-5 wt.% Al alloy coating. Alloy coated wire consists of alternative layers of zinc rich and aluminium rich phases. The performance of alloy coated wires has been evaluated by salt spray and Tafel tests. The alloy coated wire shows around 4 times improvement of corrosion performance against aggressive chloride environment compared to pure zinc coated wire. This can be attributed to the fact that aluminium rich phase prevents dissolution of zinc rich phase.     

Insulated Piston Heads for Diesel Engines

Widely studied in the 1980s, the insulation of pistons in engines aimed at reducing the heat losses and thus increasing the indicated efficiency. However, those studies stopped in the beginning of the 1990s because of NO _x emission legislation and also because of lower oil prices. Currently, with the improvement of exhaust after treatment systems (diesel particulate filter, selective catalytic reduction, and diesel oxidation catalyst) and engine technologies (exhaust gas recirculation), there are more trade-offs for NO _x reduction. In addition, the fast rise of the oil prices tends to lead back to insulation technologies in order to save fuel. A 1 mm thick plasma sprayed thermal barrier coating with a graded transition between the topcoat and the bondcoat was deposited on top of a serial piston for heavy-duty truck engines. The effects of the insulated pistons on the engine performance are also discussed, and the coating microstructure is analyzed after engine test.     

Brazing zirconium alloys with an amorphous rapidly quenched strip brazing alloy

Application of aluminum alloy, which is a typical lightweight material, has been expected to achieve energy saving and prevention of pollution in many kinds of transportation vehicles. While the structure made of whole aluminum alloy, however, is lightweight, it still has problems, such as low mechanical strength and high cost. Hence, a hybrid or joining structure made of aluminum alloy and steel seems to be reasonable because of its light weight and higher strength.

To make a hybrid structure for transportation vehicles, we examined welding by friction stirring between aluminum alloy and low-carbon steel, which could be welded without melted weld materials. As a result, welding between aluminum alloy and low-carbon steel that had a thin intermetallic compound at the weld interface was obtained.

In recent automobile manufacturing, zinc-coated steel has been used for structural parts in general. On welding between zinc-coated steel and other materials such as aluminum alloy, existence of a Zn layer between aluminum and steel has to be taken into account to get a high-quality joint between the materials.

In this study, spot joining between aluminum alloy and several kinds of zinc-coated steels by friction stirring was carried out, and the effect of the coated layer both on the weld strength and weld interface microstructure was investigated. As a result, the joint between aluminum alloy and zinc-coated steel was stronger than that between aluminum alloy and non-coated steel, when the coated layer was removed at the weld interface by plastic flow of aluminum alloy.     

柴油发动机活塞用铝基材料研究进展及失效分析

活塞作为柴油发动机的核心部件之一,恶劣的服役工况对其材料有特殊的要求。概述了活塞用铝基材料的发展状况,包括合金系(Al-Cu-Si系、Al-Cu-Ni-Mg系、共晶型Al-Si-Cu-Mg系和过共晶型A1-Si-Cu-Mg系)与复合材料系(SiC/Al基复合材料、Al_2O_3/Al基复合材料和TiC、TiB_2/Al基复合材料等),并介绍了不同材料的适用范围。同时,归纳了常见活塞铝基材料的失效机制,包括磨损、机械损伤以及顶部开裂等。其中,活塞因磨损造成的失效在统计活塞失效机制中所占比例较大,具体可分为粘着磨损失效和磨粒磨损失效。针对活塞磨损失效提出了相关改善措施,如材料成分选取和制备方法选取等。此外,针对柴油发动机在实际运行工况中,因活塞所处部位存在润滑油不完全燃烧造成的含硫、氮等腐蚀性气氛而加速磨损的问题,可依托该气氛与相应增强相的反应,使其接触表面生成自润滑膜而减少甚至抑制磨损,进而延长柴油发动机活塞的使用寿命。     

梯度复合材料活塞的挤压铸造研究

陶瓷梯度增强铝基复合材料是发动机活塞的理想增强材料。采用挤压铸造法制造出梯度复合材料活塞,对梯度 复合材料的层间结合的显微组织进行了观察,发现复合材料之间、复合材料与基体之间的结合情况非常令人满意。采用 ANSYS有限元分析软件,对梯度复合材料活塞的隔热效果进行了分析,分析结果显示隔热度提高了8.7％。     

Surface hardening of die steel by superplastic deformation of thermo-sprayed powder alloy

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Evaluation of defects in aluminum piston castings by using ultrasonics and computer tomography

Pistons used in automobile engines are made of aluminum alloy; and endurance of high pressure and high temperature is required. Recently, high strength pistons are needed to cope with the increase of pressure and temperature in the engine cylinder. A high strength piston is possible when the piston casting has little or no casting defects, such as micro-pores and cracks. Generally the defects can be evaluated by non-destructive testing (NDT), and the most efficient ways for evaluation are using ultrasonics and computer tomography. In the present study, two NDT methods were compared and evaluated to investigate the defects in the aluminum piston castings. Artificial defects were machined by using very small drill bits with diameters 1, 0.5, 0.3, 0.2 and 0.1 mm. The defects were investigated by using an ultrasonic tester and a computer tomography system. Defects smaller than 0.3 mm may not be found by using the ultrasonic test, but the defects may be found by using the computer tomography system. The investigation conditions for detecting small defects and the scanning time for in-line defect analysis are discussed in the present study.     

Influence of superficial coating of CeO2 on the oxidation behavior of AISI 304 stainless steel

The effect of a superficially-applied, cerium-oxide coating on the non-isothermal oxidation behavior of AISI 304 stainless steel in dry air has been investigated. The heating rate employed was 3 K/min up to a final temperature of 1423 K. The reactive oxide coating not only reduced the reaction rate but also facilitated scale adhesion to the alloy substrate. Post-oxidation analyses of the alloy/scale combination using optical microscopy, SEM, EDAX, and XRD provide evidence for a changeover in the mechanism of oxide growth from the scale/gas interface to the alloy/scale interface for the coated steel.     

Oxidation of Fe–22Cr Coated with Co3O4: Microstructure Evolution and the Effect of Growth Stresses

The oxidation behavior of a commercially available Fe–22Cr alloy coated with a Co₃O₄ layer by metal organic—chemical vapor deposition was investigated in air with 1% H₂O at 1,173 K and compared to the oxidation behavior of the non-coated alloy. The oxide morphology was examined with X-ray diffraction, electron microscopy, and energy dispersive X-ray spectroscopy. Cr₂O₃ developed in between the Co₃O₄ coating and the alloy, while alloying elements of the substrate were incorporated into the coating. Particular attention was devoted to possible sources of growth stresses and the effect of the growth stresses on microstructure evolution in the scales that developed on the non-coated and the coated Fe–22Cr alloy. Microstructural features suggested that scale spallation on coated Fe–22Cr occurred as a result of superimposing thermal stresses during cooling onto the growth stresses, that had developed during oxidation.     

4All铝合金活塞锻件热处理工艺研究

４Ａｌｌ铝合金是生产活塞锻件的理想材料,它具有耐磨性好、热膨胀系数小的特点。应用正交设计法找了４Ａｌｌ铝合金最佳热处理工艺制度,使活塞锻件的综合性能得到提高,避免了使用中脆性断裂现象。     

MoB/CoCr Cermet Coatings by HVOF Spraying against Erosion by Molten Al-Zn Alloy

MoB/CoCr, a novel cermet material for thermal spraying, with high durability in molten alloys has been developed to utilize for aluminum die-casting parts, and for hot continuous dipping rolls in Zn and Al-Zn plating lines. The durability of the MoB/CoCr coatings prepared by high velocity oxy-fuel (HVOF) spraying has been investigated using a molten-metal immersion tester. The tests revealed that the MoB/CoCr coating has much higher durability without dissolution in the molten Al-45wt.%Zn alloy. Little change of crystal structure, mainly composed of double borides of CoMoB and CoMo₂B₂, is observed after the immersion test, suggesting that the double borides have much higher durability. Using undercoat is effective to reduce the influence of large difference in thermal expansion between the MoB/CoCr topcoat and substrate of stainless steel of AISI 316L, widely used for the hot continuous dipping rolls. Optimized thickness combinations of topcoat and undercoat are necessary to obtain intrinsic performance of low reactive MoB/CoCr against the molten Al-45wt.%Zn alloy.