Effect of Aging on Abrasive Wear of Deformable Aluminum Alloy AA6351

Special features of abrasive wear of deformable aluminum alloy AA6351 are studied as a function of aging conditions and modes of friction tests. After aging in different modes the specimens are tested for wear in a special installation by the method of “brad against disk” with the use of abrasives with different grain sizes. The effects of different speeds of sliding and loads on the wear resistance and surface roughness are studied.     

基于钎焊涂覆的树脂结合剂金刚石砂轮及性能研究

利用钎焊方法对单晶RVD和多晶PDGF1 2种金刚石磨料表面进行涂覆,制备涂覆前后4种磨料的树脂结合剂金刚石砂轮。研究钎焊过程对金刚石磨粒表面形貌和力学性能的影响,并测试不同砂轮加工硬质合金时的磨削性能。结果表明:钎焊涂覆方法可以在金刚石磨料表面有效包覆一层钎料合金涂层,涂层与金刚石磨粒间形成TiC界面结合。与涂覆前磨粒相比,涂覆后RVD磨粒的冲击韧性(TI)值减小了6%,PDGF1磨粒的TI值增大了42%。用钎焊涂覆PDGF1磨料制作的树脂结合剂金刚石砂轮拥有更低的磨削力和更高的磨削比, 但用钎焊涂覆RVD磨料制作的树脂结合剂金刚石砂轮的结果则相反。在相同加工参数下,4种砂轮磨削硬质合金的表面形貌相似,其表面粗糙度在0.50～0.68 μm。      

自制聚氨酯磨棒磨削合金灰口铸铁的表面粗糙度实验研究

为研究聚氨酯磨棒对合金灰口铸铁表面磨削质量的影响机制,自制了聚氨酯磨棒,并在磨棒中分别添加粒径为1、6和9μm的金刚石磨粒对合金灰口铸铁进行磨削加工,利用光学显微镜和白光干涉仪对磨削加工后的合金灰口铸铁表面形貌及平均表面粗糙度R_a进行分析比较。结果表明:使用粒径9μm的金刚石磨粒磨削工件表面,其磨削痕迹较深,表面粗糙度较差;相比之下,使用粒径6μm的金刚石磨粒磨削工件,可得到最佳的表面粗糙度,其R_a值可达0.01μm;而使用粒径1μm的金刚石磨粒,其磨削能力最差,材料被推挤到磨料的两侧,造成实际的表面粗糙度不够理想。     

An integrated study on the effect of pre- and post-extrusion heat treatments and surface treatment on the filiform corrosion properties of an aluminium extrusion alloy

The effect of pre- and post-extrusion heat treatments on the filiform corrosion behaviour of a well-known aluminium extrusion alloy AA6063 is studied by a combination of accelerated filiform corrosion exposure tests and potentiodynamic polarisation measurements for four different surface treatments. It is shown that the post-extrusion heat treatment of this AlMgSi alloy can influence the filiform corrosion properties significantly, in particular for the milder surface treatments. In contrast, the relative effect of the pre-extrusion treatment on the filiform corrosion properties is minimal for all treatments. The alloys are most susceptible to filiform corrosion in the β′ condition. The susceptibility decreases with coarsening of the Mg₂Si particle distribution. For the post-extrusion heat and surface treated AA6063 material a clear correlation between the polarisation characteristics and the two principal filiform corrosion characteristics, i.e. the propagation rate and total area of attack after accelerated exposure, is observed. The observed correlation is attributed to a pitting corrosion mechanism with a rate depending on the (coupled) Mg₂Si precipitate size and fraction.     

Microstructure-dependent corrosion of herringbone-grooved embossed Al–1.1 wt% Mn strips for heat exchanger tubes

This paper studied the effect of embossing on the microstructure and corrosion behaviour of an Al−1.1 wt% Mn sheet. The microstructure of the embossed Al−1.1 wt% Mn sheets was studied by differential interference contrast microscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, focused ion beam microscopy and X-ray computational tomography. Finite element modelling was used to assess the stress and strain distribution developed during embossing, and to support the experimental analyses. The corrosion behaviour of the embossed sheets was assessed using potentiodynamic anodic polarisation tests, followed by corrosion surface morphology analysis. Results showed a microstructural evolution of the alloy during embossing, which is dependent on both the embossed pattern geometry and the roll forming direction. Nonsymmetrical displacement of material, in respect to the pattern geometry, was caused by the anisotropic forming pressure applied on the strip during roll forming, which yielded the formation of more susceptible sites for pitting and intergranular corrosion on the embossed aluminium surfaces.     

Pitting corrosion of rheocast A356 aluminium alloy in 3.5 wt.% NaCl solution

In this study, the microstructure and corrosion behaviour of rheocast and gravity-cast A356 aluminium alloys were examined and compared. Scanning Kelvin probe force microscopy (SKPFM) results proved that large potential differences between iron-containing intermetallics and the α-Al matrix were responsible for the initiation of the attack at the intermetallics/α-Al interfaces. For longer immersion times, corrosion attack proceeded through the eutectic areas. Semisolid processing refined the eutectic silicon and iron-intermetallics and reduced the potential difference between secondary phases and the matrix. This resulted in improved pitting corrosion resistance of the rheocast A356 aluminium alloy.     

Influence of casting defects on fatigue behaviour of A356 aluminium alloy

Abstract

The fatigue behaviour of A356 cast aluminium alloy under 10⁴ cycles was investigated by a servo-hydraulic machine at the temperature of 150°C. The specimens for the fully reversible tension compression tests were cut from cylinder head castings of automobile engines. The testing data were treated by S–N curve and the staircase method and the mean values of fatigue property coincided with each other by these two methods, though the data scattered with different casting defects. The fracture surfaces of fatigue specimens were examined by OM, SEM and EDS. It was found that in most of the specimens two or more fatigue crack initiations appeared at a fracture surface. Compared with casting defects such as oxide film, inclusion and blowhole, shrinkage porosity is more detrimental to the fatigue behaviour of aluminium alloy castings.     

Fine finishing of internal surfaces using elastic abrasives

The paper describes a simple and innovative approach of using elastic abrasives for generating ultra fine finish on internal surfaces of tubular specimens. Elastic abrasive is a unique concept of using abrasive embedded elastomeric balls having the special capability to deform in conformity to work surface and thereby imparting a very fine refinement of its profile without altering the form. The mechanism of material removal in the proposed methodology is analysed using a mathematical model and its validation was done using a systematic experimentation procedure. Response surface methodology using central composite design is applied for the experimental study to investigate the effect of axial pressure, abrasive grain size and longitudinal stroke velocity of elastic abrasives on the surface finish. The process discussed in this paper is a simple and cost effective option to produce micro/nano-finish on the internal surfaces of a wide range of industrial components including hollow specimens, high aspect ratio bores and sleeves.     

Influence of kinematics and abrasive configuration on the grinding process of glass

The micro- and macro-kinematics performed by the abrasives play a key role during the grinding of brittle materials. The present work intends to evaluate the influence of the abrasive configuration and the trajectory of the abrasive tool on the grinding process of glass. For this purpose, two different arrangements of abrasive pins were tested under three different kinematic curves: two epitrochoidal and one hypotrochoid. Grinding tests were carried out on commercial glass tiles, using 1 h of grinding time and water as lubricant. Computational simulations were used to quantify the spatial distribution of abrasive contacts over the sample surface, including the scratching orientation of each abrasive contact. The amount of material removed from the surface due to the grinding was measured by contour profilometry. By assembling the results from both experiments and simulations the average removal rate of the grinding process were determined and mapped for the entire abraded surface. The effect of the abrasive configuration was found to be either minimized or maximized according to the kinematics chosen, and differences of up to 30% were detected.     

Modelling the corrosion behaviour of Al2CuMg coarse particles in copper-rich aluminium alloys

The corrosion behaviour of 2024 aluminium alloy in sulphate solutions was studied; attention was focused on the influence of coarse intermetallic Al₂CuMg particles on the corrosion resistance of the alloy. Model alloys representative of the aluminium matrix and of Al₂CuMg coarse intermetallics were synthesized by magnetron sputtering. Open-circuit potential measurements, current-potential curve plotting and galvanic coupling tests were performed in sulphate solutions with or without chlorides. Further explanations were deduced from the study of the passive films grown on model alloys in sulphate solutions. The results showed that model alloys are a powerful tool to study the corrosion behaviour of aluminium alloys.     

Surface Treatments for Enhanced Wear Resistance of Aluminium

This report presents a survey of various surface treatments to improve the wear resistance of aluminium. Over 25 different treatments have been produced and evaluated in laboratory and in application tests. Three plastically formable alloys and one pressure die casting alloy were included.

The different coating systems have been characterised with respect to structure and morphology by scanning and transmission electron microscopy. The laboratory wear tests were performed by using Taber abraser and pin on disc as standard methods. As a comparison, a non-standard reciprocating adhesive wear test set-up was used. In addition, a corrosion test by accelerated outdoor exposure (SCAB) was performed. The application tests were a rotating PTFE sealed sleeve, a station chain in a food packing machine and a yarn feeder.

The results from the abrasive and adhesive laboratory wear tests have been correlated to the results in the application tests. For some of the evaluated coating systems the correlation between the laboratory and the application tests is reasonably good. However, substantial difference in performance was found for other systems.     

CBN磁性磨料磁力研磨TC4钛合金工艺参数优化

为提高磁力研磨TC4钛合金的研磨效果,采用了一种新型CBN磁性磨料,通过正交试验法对磁力研磨TC4钛合金试验中各工艺参数进行优化,并通过试验评价新型CBN磁性磨料的结合强度和研磨能力。结果表明:优化工艺参数为:进给速度1mm/min、主轴转速1500r/min、加工间隙1mm和磨料填充量2.5g。在采用CBN磁性磨料和最优工艺参数组合下,钛合金工件经过30min研磨表面粗糙度从0.330μm下降到0.098μm,表面质量明显提高。研磨60min后磁性磨料未出现磨料脱落和破碎现象,磨料结合十分牢固。     

Corrosion behaviour of aircraft coating systems in acetate- and formate-based de-icing chemicals

Corrosion behaviour of four coating systems, which are commonly used in aircraft components; namely cadmium-coated and subsequently chromate-treated steel AISI 4340, aluminium-coated steel AISI 4340, anodised aluminium alloy 7075-T6 and chromate-treated aluminium alloy 7075-T6, were investigated in six commercial acetate- and formate-based de-icing chemicals. The results show that the aluminium-coated steel specimens experience least corrosion among the four coating systems; no corrosion is detected in potassium acetate-based de-icing chemicals (Safeway KA HOT, Safegrip and Safegrip+), although some corrosion is observed in the other three chemicals (Safeway SD, Safeway SF and Meltium). In contrast, the coatings in the other three coating systems are damaged in all six de-icing chemicals. The thickness of the coating does not necessarily predict how well the coating will protect the substrate; the thickest coating, several tens of micrometres, is apparent on the cadmium- and chromate-coated steel specimens, while only a few micrometres thin aluminium coating on the steel substrate is the only coating system that can survive the corrosion tests in some of the de-icing chemicals. Comparison of the results from the two test methods used in this research, polarisation measurements and chemical exposure tests, shows that, for each coating system, the extent of corrosion, as evaluated on the basis of weight changes calculated from corrosion current density values and those experienced during chemical exposure tests, is different: the weight changes that materialise during exposure tests are, at least, from one to two orders of magnitude higher than those predicted by calculations. In this paper, these observations are discussed and explanations for them are presented.     

The effect of heat treatment on the corrosion behaviour of 319 aluminium alloy

The effect of various heat treatments on the corrosion behaviour of 319 T1 cast aluminium alloy was investigated. From this alloy, specimens were heat treated in T5, T6 and two steps solution heat treatment T6 conditions and afterwards were subjected to electrochemical corrosion in a 0.1 M NaCl solution (pH = 12). From the above treatments, T5 heat treatment did not improve the corrosion resistance of the as‐received alloy in contrast to T6 heat treatment which improved the corrosion resistance of the same alloy. However, two steps solutionizing T6 treatment showed the best corrosion resistance of the aluminium alloy.     

Corrosion behaviour of AA2024 aluminium alloy in different tempers in NaCl solution and with the CeCl3 corrosion inhibitor

The paper analyses the corrosion behaviour of naturally and artificially aged AA2024 alloy in NaCl solution and in the presence of an environment-friendly corrosion inhibitor, CeCl₃. On the basis of the values of polarisation resistance and corrosion current density, the corrosion resistance of the protective inhibitor film is established as well as the general corrosion resistance of this aluminium alloy. Resistance to pit formation is determined based on the difference in pitting and corrosion potentials while resistance to pit growth is determined based on the amount of charge consumed during pit growth. A scanning electron microscope is used to examine the morphology of the pits formed during the pitting corrosion testing, as well as to determine the cerium content on intermetallic particles and the matrix AA2024 alloy. The corrosion behaviour of AA2024 alloy is investigated after different test periods in NaCl solution and in the same solution with the CeCl₃ inhibitor. The corrosion resistance of both tempers of AA2024 alloy is more than one order of magnitude higher in the presence of CeCl₃. An explanation of the observed differences in the corrosion behaviour of the naturally and artificially aged AA2024 alloy is proposed. Different corrosion behaviour of the alloy after different test periods is also explained.     

The corrosion of steel and aluminium in calcium chloride/ammonia,magnesium chloride/methylamine and magnesium chloride/methylamine/decane

The corrosion of St 37, StE 36, Al 99,5 and Al-Mg 3 in the chemical pairs of substances calcium chloride/ammonia, magnesium chloride/methylamine and magnesium chloride/methylamine/decane was investigated. The corrosion tests were performed in autoclaves at room temperature to 180 °C. The nominal duration of the experiments was 1000 hours. Rod shaped fatigue specimens with polished surfaces served as test specimens; these were fatigue tested after the corrosion treatments. All materials tested were compatible with calcium chloride/ammonia under the experimental conditions employed. Steel and aluminium showed similar behaviour against magnesium chloride/methylamine and magnesiumchloride/methylamine/decane, respectively. At room temperature and 70°C to 80°C the corrosion of steel and aluminium was low (wall losses in the order of 1 m?m/a). Corrosion increased with increasing temperature. The activation energy for the reaction, which determined the rate of weight loss in magnesium chloride/methylamine/decane, was AE_st = 0, 60 ± 0,18 eV for steel, and AE_Al = 1, 07 ± 0,07 eV for aluminium. A corrosion treatment on aluminum fatigue specimens after 1000-1500 hours at 110 °C caused a notable decrease in fatigue strength; no such behaviour was noted for steel, even when corroded at 170 °C.     

W-Mo-Cr合金对金刚石砂轮磨块的摩擦化学修整

为解决粗磨粒金刚石砂轮磨块的修整问题,使用W-Mo-Cr合金材料作为修整工具对磨粒粒度尺寸为297~420μm的金刚石砂轮磨块进行修整,修整前后分别测量砂轮表面磨粒的等高性和磨粒的微观形貌,并且分别用修整前后的砂轮磨块进行WC硬质合金的磨削试验。结果表明:W-Mo-Cr合金材料对金刚石砂轮修整效率高,修整后砂轮表面磨粒的等高性提升了60%左右。利用修整后的金刚石砂轮磨削WC硬质合金,工件表面质量得到很大的改善,表面粗糙度达到R_a0.149μm。      

The effect of ion implantation on the corrosion behaviour of pure iron—II. Chromium ion implantation

As part of a programme to investigate the effect of ion implantation on the corrosion behaviour of iron, pure iron specimens have been implanted with doses of 5 × 10¹⁴ and 2 × 10¹⁵ chromium ions/mm². Using a three-sweep potentiokinetic polarization technique the corrosion behaviour of these surface alloy layers has been compared with that of conventional binary FeCr alloys containing from 0.8 to 12.5 wt%Cr. It was found that apart from a slight thickening of the air-formed oxide film induced by the ion implantation process, the polarization behaviour of conventional alloys and of alloys produced by ion implantation was qualitatively very similar. Quantitatively the low dose chromium implanted specimens corresponded to a conventional Fe-4.9%Cr alloy while the high dose chromium implanted specimens resembled conventional alloys containing x12.5%Cr. These data provide a sound basis for the interpretation of the potentiokinetic polarization and corrosion behaviour of the novel surface alloy layers which can be produced by ion implantation.     

Influence of testing parameters on the corrosion rate of magnesium alloys

In sodium chloride solutions alloy composition, phases, microstructure and grain size influence the corrosion behaviour of magnesium alloys. Concentration and distribution of the critical impurities iron, nickel and copper affect the corrosion performance strongly. Salt spray tests according to ASTM B 117 or DIN 50021 are used to control quality of magnesium alloys. Results of these tests often estimate alloy subcontractors and are therefore very important to placing. Standards specify test solution, test temperature and position of specimens during test in the salt spray chamber. Standards not prescribe preparation of test specimens, exposure period, handling of the specimens after salt spray test nor the interpretation of the results. Results of salt spray tests can be only compared, provided that test conditions are exactly given. Whether the standards fulfil the above described criteria, will be shown by extensive investigations. Therefore the influence of exposure period, surface condition and microstructure was investigated.     

金属/金刚石复合磨料在树脂磨具中的应用

为改善砂轮磨削钢轨的性能,通过热压烧结再固化的方法制备超硬复合磨料树脂磨具试验样条,考察不同种类的复合磨料对样条抗弯强度、抗冲击强度及磨具磨耗比的影响,并用电镜观察磨削后磨具及钢轨对磨件的形貌,表征磨削表面质量。结果显示:超硬磨料与金属结合剂造粒后,抗弯强度、抗冲击强度、磨耗比均得到明显提高,最大分别提高50%、近2倍和约12.6倍。超硬材料以复合磨料的形式添加可提高磨具对磨料的把持力,减少钢轨发蓝、烧伤等现象,提高轨面质量。