Validation of a systematic approach to modeling spray quenching of aluminum alloy extrusions, composites, and continuous castings

Optimal cooling of aluminum alloys following the high- temperature extrusion process suppresses precipitation of intermetallic compounds and results in a part capable of possessing maximum strength and hardness after the subsequent age- hardening process. Rapid quenching suppresses precipitation but can lead to large spatial temperature gradients in complex- shaped parts, causing distortion, cracking, high residual stress, and/or nonuniform mechanical properties. Conversely, slow cooling significantly reduces or eliminates these undesirable conditions but allows considerable precipitation, resulting in low strength, soft spots, and/or low corrosion resistance. This study presents a systematic method of locating and operating multiple spray nozzles for any shaped extrusion such that uniform, rapid cooling and superior mechanical and metallurgical properties are achieved. A spray nozzle data base was compiled by measuring the distribution of spray hydrodynamic parameters (volumetric spray flux, mean drop diameter, and mean drop velocity) throughout the spray field of various industrial nozzles. Spray heat transfer correlations, which link the local spray hydrodynamic parameters to the heat transfer rate in each of the boiling regimes experienced by the surface, defined the spatially nonuniform boundary conditions in a numerical model of the quenching process that also accounted for interference between adjacent spray fields. New correlations, offering increased accuracy and less computational time, were formulated for the high- temperature boiling regimes which have a critical influence on final mechanical properties. The quench factor technique related predicted thermal history to metallurgical transformations occurring within the extrusion to predict hardness distribution. The validity of this unique approach was demonstrated by comparing model predictions to the temperature response (and hardness after artificial aging) of an L- shaped Al 2024- T6 extrusion to quenches with multiple, overlapping water sprays. The validation study reported herein concludes by exploring the possibility of applying quenching technology to improving the properties of extruded metal- matrix composites such as SiC_p/Al 6061 and cast alloys.     

Determination of heat transfer coefficient for forging applications

A setup for measuring the contact heat transfer coefficient between a tool steel die and a specimen was designed, developed, and fabricated. A microcomputer was programmed to collect and process the temperature data. Tests were conducted under dry and lubricated conditions at different temperatures and pressures on four aluminum alloys, namely, 2024-T4, 2024-O, 6061-O, and 1100-O. MoS₂ was used as the lubricant. Results indicate that the heat transfer coefficient increases with pressure and decreases with specimen yield strength. Variation in heat transfer coefficient with temperature is due to chemical changes which occur in the lubricant at the test temperature. The heat transfer coefficient was an order of magnitude greater at high pressures than at nominally zero pressure.     

Dry and clean age hardening of aluminum alloys by high-pressure gas quenching

When precipitation-hardenable aluminum parts are water quenched, distortion occurs due to thermal stresses. Thereby, a costly reworking is necessary, and for this reason polymer quenchants are often used to reduce distortion, with the disadvantage that the quenched parts have to be cleaned after quenching. In opposition to liquid quenchants, gas quenching may decrease distortion due to the better temperature uniformity during quenching. Furthermore, cleaning of the quenched parts can be avoided because it is a dry process. For this purpose, a heat-treating process was evaluated that included a high-pressure gasquenching step. Gas quenching was applied to different aluminum alloys (i.e., 2024, 6013, 7075, and A357.0), and tensile tests have been carried out to determine the mechanical properties after solution annealing, gas quenching, and aging. Besides high-pressure gas quenching, alloy 2024 was quenched at ambient pressure in a gas nozzle field. The high velocity at the gas outlet leads to an accelerated cooling of the aluminum alloy in this case. Aluminum castings and forgings can be classified as an interesting field of application of these quenching methods due to their near-net shape before the heat treatment. Cost savings would be possible due to the reduced distortion, and therefore, less reworking after the precipitation hardening.     

Corrosion protection of AA 2024-T3 by bis-[3-(triethoxysilyl)propyl]tetrasulfide in neutral sodium chloride solution. Part 1: corrosion of AA 2024-T3

This study consists of two parts. In the first part, the corrosion of 2024-T3 aluminum alloy (AA 2024-T3) was studied using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that the anodic S phase (Al₂CuMg) particles dealloyed Al and Mg during the 3.5 h of immersion in a neutral 0.6 M sodium chloride (NaCl) solution; with the dealloying of Mg being the most severe. Simultaneously, a heavy dissolution was also observed for the surrounding Al matrix of the S phase particles. This Al dissolution is likely to be caused by a local alkalization resulting from the coupled cathodic reaction (water and/or oxygen reduction). Such corrosion in AA 2024-T3, however, can be inhibited efficiently after the treatment of bis-[3-(triethoxysilyl)propyl]tetrasulfide (bis-sulfur silane). The associated studies on bis-sulfur silane treated AA 2024-T3 will be presented in the second part.     

Effects of fluidised bed quenching on heat treating characteristics of cast Al–Si–Mg and Al–Si–Mg–Cu alloys

Abstract

The quench sensitivity of Al–Si–Mg (D357 unmodified and Sr modified), and Al–Si–Mg–-Cu (354 and 319 Sr modified) cast alloys was investigated using a fluidised bed (FB). The average cooling rate of castings in the fluidised bed is lower than those quenched in water; the cooling rate first increases to a certain maximum and then decreases during quenching. The change in the cooling rate during quenching in water was more drastic, where the cooling rate varied from 0 to ?80 K s^?1 in less than 8 s, as compared with those quenched in FB, where the cooling rate varied from 0 to ?14 K s^?1 in 18 s. The FB quenching resulted in the formation of several metastable phases in Al–Si–Mg–Cu alloys; in contrast, no such transformation was observed during water quenching. The T4 yield strength of the FB quenched alloys was greater than water quenched alloys owing to the formation of a greater volume fraction of metastable phases in the FB quenched alloys. The tensile properties of T6 treated alloys show that Al–Si–Mg alloys (both unmodified and Sr modified) are more quench sensitive than Al–Si–Mg–Cu alloys. The high quench sensitivity of the Al–Si–Mg alloys is because GP zones are not formed, whereas GP zones are formed during quenching of the Al–Si–Mg–Cu alloys as predicted by time temperature transformation and continuous cooling transformation) diagrams.     

Oxide formation on aluminium alloys in boiling deionised water and NaCl, CeCl3 and CrCl3 solutions

Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy have been employed to provide depth, surface chemical and morphological information respectively for a range of Al-alloys treated for 2 h at 90-100 °C in either deionised water (DIW), 30 mM NaCl, 10 mM CeCl₃ or 10 mM CrCl₃ solutions. Alloys included Al sheet 1100-O, 2024-T3, 3004-H19, 5005-O, 6061-T6 and 7075-T6. In DIW all alloys developed the same oxide thickness with a boehmite-like appearance. In NaCl and CeCl₃ solutions the oxide thickness varied with alloy composition but was considerably thicker than the deionised case and maintained a boehmite-like appearance. Ce was distributed throughout the oxide but at low levels. In all cases some Ce^IV was detected on the surface of the oxide, the remainder being Ce^III. In CrCl₃ solution, the oxide thickness was extremely thin with the appearance of a dense oxide rather than a boehmite-type structure.     

Experimental observation and analysis of burr formation mechanisms in face milling of aluminum alloys

The purpose of this paper is to study the burr formation mechanisms in face milling process, and to investigate the influence of cutting conditions on burr formation in face milling of aluminum alloys. The fly milling cutter is used to carry out single-tooth face milling tests. Three aluminum alloys were tested: Al 1100 (cold drawn), Al 2024-T4 and Al 6061-T6. It is found that the burr geometry is strongly dependent upon the in-plane exit angle. Five types of burrs were observed in the experiments: knife-type, wave-type burr, curl-type, edge breakout and secondary burr. Formation mechanisms of each type of these burrs are discussed in details. The relationship between their existence and the machining condition is indicated. The machining guideline in face milling is given at the end of the paper to reduce burr size effectively through the formation of secondary burr.     

Wear behaviors of pure aluminum and extruded aluminum alloy (AA2024-T4) under variable vertical loads and linear speeds

The aim of this study was to investigate the transition of wear behavior for pure aluminum and extruded aluminum alloy 2024-T4 (AA2024-T4). The wear test was carried using a ball-on-disc wear testing machine at various vertical loads and linear speeds. The transition of wear behaviors was analyzed based on the microstructure, wear tracks, wear cross-section, and wear debris. The critical wear rates for each material are occurred at lower linear speed for each vertical load. The transition of wear behavior was observed in which abrasion wears with the generation of an oxide layer, fracture of oxide layer, adhesion wear, severe adhesion wear, and the generation of seizure occurred in sequence. In case of the pure aluminum, the change of wear debris occurred in the order of blocky, flake, and needle-like debris. Cutting chip, flake-like, and coarse flake-like debris was occurred in sequence for the extruded AA2024-T4. The transition in the wear behavior of extruded AA2024-T4 occurred slower than in pure aluminum.     

2024-T3铝合金在硫酸-硼酸-磷酸中的阳极氧化和腐蚀行为

在含有10%硫酸、5%硼酸和2%磷酸的混合电解液中,对2024-T3铝合金进行阳极氧化处理,以提高其耐腐蚀性能。使用电化学阻抗频谱分析研究阳极氧化处理后合金的腐蚀行为。利用塔菲尔图和盐水喷雾技术进行对比发现,与只用磷酸或硫酸和硼酸的电解液相比,使用含有10%硫酸、5%硼酸和2%磷酸的混合电解液阳极氧化处理后的2024-T3铝合金,具有更好的耐腐蚀性和持久性。该电解液可以替代普遍用于阳极氧化铝合金的铬酸盐浴。     

Corrosion inhibition performance of polypyrrole Al flake composite coatings for Al alloys

Polypyrrole (PPy) was deposited on Al flakes in the presence of oxyanions (molybdate, phosphate or vanadate) as inhibiting dopants and the PPy modified Al flakes were incorporated into an epoxy primer as protection pigments for AA 2024-T3. The protection performance of the PPy Al flake coating was assessed by electrochemical evaluations including Scanning Vibrating Electrode Technique (SVET), Electrochemical Impedance Spectroscopy (EIS) and salt spray test. The oxyanion doped PPy Al flake coating shows enhanced protection performance for AA 2024-T3. An oxygen scavenger protection mechanism is suggested for PPy in the composite coating, and the roles of Al flake and oxyanions in the formulation are discussed.     

211Z高强韧耐热铝合金的淬透性研究

采用类端淬设备、电导率计、差示热扫描分析仪和透射电镜等并结合数字模拟研究了211Z型铝合金的淬透性能。结果表明:试样在≤40℃水温淬火的过饱和固溶程度、时效后的硬度均高于水温较高(50~60℃)时淬火的相应值,但淬透深度相反;试样时效处理后的硬度值受淬火敏感温度区间(140~380℃)的平均冷却速度影响,超过临界值后,硬度值基本保持不变,小于临界值,则随平均冷却速度的增加而增大。     

Effects of testing variables on stress corrosion cracking susceptibility of Al 2024-T351

In the present study, the effects of testing variables on stress corrosion cracking (SCC) susceptibility of Al 2024-T351 in 3.5% NaCl solution were examined using slow strain rate test (SSRT) method with controlled applied potentials and a constant load test (CLT) method. The SSRTs were conducted at various strain rates and applied potential, while the CLTs were performed with different exposure time, with different grain directions of ST (short-transverse) and L (longitudinal) to understand how the testing parameters affected on the SCC susceptibility of Al 2024-T351. The percent reductions in tensile elongation in an SCC-causing environment over those in air tended to express the SCC susceptibility of Al 2024-T351 most properly for both SSRT and CLT. The present fractographic examination suggested that both anodic dissolution and hydrogen embrittlement played a role in the SCC process of Al 2024-T351 in 3.5% NaCl solution at both anodic and cathodic applied potentials, and the contribution of each mechanism could vary with different testing variables. It was also found that the SCC susceptibility of Al 2024-T351 obtained from the CLT result could provide the similar SCC evaluation result obtained by SSRT with a proper selection of testing variables. The metallurgical aspect of SCC behaviour of Al 2024-T351 was also discussed based on the microstructural and fractographic examinations.     

Characterization of atmospheric corrosion in Al/Ag lap joints

Lap joints fabricated using Al2024T3/commercially pure Ag sheet couples with nylon fasteners were exposed to standard field tests in a tropical marine atmosphere for a total period of six months. Atmospheric conditions were recorded using a weather monitoring station. Simultaneously, samples were also exposed in a salt spray chamber according to ASTM B117 and GM 9540P standards. Corrosion data was obtained for monthly intervals for both field and laboratory samples. Weight loss, pitting characteristics and the nature of the corrosion products were evaluated. Corrosion mechanisms based on the observed atmospheric corrosion phenomena are proposed.     

2024-T4铝合金水下搅拌摩擦焊接研究

分别在空气和循环水冷条件下对2024-T4铝合金板进行搅拌摩擦焊接(friction stir welding,FSW),研究了水冷介质对FSW接头组织性能的影响.结果表明:循环水冷介质具有明显的瞬时快冷作用,水冷介质下FSW可以显著细化晶粒,并抑制焊核区析出相的生长,焊核区的平均晶粒尺寸达到700 nm,析出相尺寸达到30～200 nm.水冷介质减弱了FSW接头的热软化效应,改善了接头的组织和性能,使焊核区HV显微硬度值提高了234 MPa,接头抗拉强度提高了52.2 MPa,但试样延伸率有所下降.     

Quenching of aerospace forgings from high temperatures using air-assisted, atomized water sprays

The nickel-based superalloy or titanium materials used in the aerospace industry are cooled from high temperatures during the heat treatment process to obtain appropriate strength properties. However, unacceptably high residual stresses can be developed in some situations if the rate of cooling is too high so that air-assisted, atomized water sprays have been suggested as an alternative to the widely used techniques of quenching in oil or water. Thus, this article examines two aspects of the use of air-water sprays for quenching aeroengine forgings. First, basic experimental heat transfer data are presented for a wide range of water flows and for surface temperatures up to approximately 850 °C, for both plane and recessed surfaces. Second, the heat transfer data are used in numerical simulations to study the influence of nonuniform spray distributions on the residual stress patterns in a typical forging. This paper was presented at the ASM Third International Conference on Quenching and Control of Distortion, 24–26 March 1999, in Prague, Czech Republic.     

Effect of the Cold-Sprayed Aluminum Coating-Substrate Interface Morphology on Bond Strength for Aircraft Repair Application

This article is dealing with the effects of surface preparation of the substrate on aluminum cold-sprayed coating bond strength. Different sets of AA2024-T3 specimens have been coated with pure Al 1050 feedstock powder, using a conventional cold spray coating technique. The sets were grit-blasted (GB) before coating. The study focuses on substrate surface topography evolution before coating and coating-substrate interface morphology after coating. To study coating adhesion by LASAT^® technique for each set, specimens with and without preceding GB treatment were tested in load-controlled conditions. Then, several techniques were used to evaluate the effects of substrate surface treatment on the final coating mechanical properties. Irregularities induced by the GB treatment modify significantly the interface morphology. Results showed that particle anchoring was improved dramatically by the presence of craters. The substrate surface was characterized by numerous anchors. Numerical simulation results exhibited the increasing deformation of particle onto the grit-blasted surface. In addition, results showed a strong relationship between the coating-substrate bond strength on the deposited material and surface preparation.     

淬火介质对7050铝合金末端淬特性的影响

采用室温水和浓度为20%的PAG水溶液(聚烷撑二醇聚合物)作为淬火介质进行Jominy末端淬火实验,用于评价7050铝合金淬透性;监测合金固溶和淬火过程中的升温速率和冷却速率,测定距淬火端不同距离的合金的淬火态电导率和时效态硬度,观察室温水淬火试样不同位置晶内淬火析出相.结果表明:采用室温水和20%PAG进行末端淬火时,合金的淬透深度分别约为65和40mm;采用PAG淬火可使合金温度快速通过淬火敏感区间,同时在淬火敏感区间外降低合金的冷却速率,使试样淬火端和中间部位合金的温度差减小.随着距淬火端距离的增加,淬火诱发析出的η平衡相的尺寸和体积分数增加,无析出区宽化.     

Impact resistance of lightweight hybrid structures for gas turbine engine fan containment applications

The ballistic impact resistance of hybrid composite sandwich structures was evaluated with the ultimate goal of developing new materials or structures for potential gas turbine engine, fan containment applications. The sandwich structures investigated consisted of GLARE-5 (Aviation Equipment, Inc., Costa Mesa, CA) laminates as face sheets with lightweight cellular metallic materials such as honeycomb, foam, and lattice block as a core material. The impact resistance of these hybrid sandwich structures was compared with GLARE-5 laminates and 2024-T3 Al sheets, which were tested as a function of areal weight (material thickness). The GLARE-5 laminates exhibited comparable impact properties to that of 2024-T3 Al at low areal weights, even though there were significant differences in the static tensile properties of these materials. The GLARE-5, however, did have a greater ballistic limit than straight aluminum sheet at higher areal weights. Furthermore, there is up to a 25% advantage in ballistic limit for the GLARE-5/foam sandwich structures compared with straight 2024-T3 Al. But no advantage in ballistic limit was observed between any of the hybrid sandwich structures and thicker versions of GLARE-5. Recommendations for future work are provided, based on these preliminary data.     

环保型淬火工艺对厚壁L80-13Cr钢管组织和性能的影响

对厚壁L80-13Cr无缝钢管进行1000 ℃保温150 min奥氏体化处理,分别采用风冷工艺、浸入水冷工艺和水雾冷却工艺进行冷却,然后在710 ℃下保温200 min进行回火。采用显微组织观察和力学性能测试等手段研究了3种淬火介质对厚壁L80-13Cr无缝钢管显微组织和力学性能的影响。结果表明:3种淬火介质的冷却性能由高到低分别是浸入水冷工艺、水雾冷却、风冷工艺;强度和冲击吸收能量都随着冷却速度的加快而提高,风冷工艺淬火的冲击吸收能量平均值为23.67 J,抗拉强度为764 MPa,水雾冷却工艺淬火的冲击吸收能量平均值为42.00 J,抗拉强度为787 MPa;浸入水冷工艺淬火的冲击吸收能量平均值为50.33 J,抗拉强度为800 MPa。但是浸入水冷工艺淬火容易有淬火裂纹,导致材料报废;雾化冷却工艺淬火,组织细小均匀,性能优异,是最合适的淬火冷却方式。     

Computation of synthetic surface heat transfer coefficient of 7B50 ultra-high-strength aluminum alloy during spray quenching

According to inverse heat transfer theory, the evolutions of synthetic surface heat transfer coefficient (SSHTC) of the quenching surface of 7B50 alloy during water-spray quenching were simulated by the ProCAST software based on accurate cooling curves measured by the modified Jominy specimen and temperature-dependent thermo-physical properties of 7B50 alloy calculated using the JMatPro software. Results show that the average cooling rate at 6 mm from the quenching surface and 420–230 °C (quench sensitive temperature range) is 45.78 °C/s. The peak-value of the SSHTC is 69 kW/(m²·K) obtained at spray quenching for 0.4 s and the corresponding temperature of the quenching surface is 160 °C. In the initial stage of spray quenching, the phenomenon called “temperature plateau” appears on the cooling curve of the quenching surface. The temperature range of this plateau is 160–170 °C with the duration about 3 s. During the temperature plateau, heat transfer mechanism of the quenching surface transforms from nucleate boiling regime to single-phase convective regime.