Effect of equal-channel angular extrusion on mechanical and wear properties of eutectic Al–12Si alloy

Mechanical and wear properties of severely deformed Al–12Si alloy by equal-channel angular extrusion/pressing (ECAE/P) were investigated. Multi-pass ECAE processing of the as-cast alloy substantially increased both its strength and ductility. The increase in the tensile and yield strength values after six ECAE passes were about 48% and 87%, respectively. The sample after six ECAE passes exhibited 10% elongation before rupture, which was about five times higher than that of the as-cast one. The improvement in both strength and ductility was mainly attributed to the changes of the shape, size and distribution of the eutectic silicon particles along with the breakage and refined of the large α-Al grains during multi-pass ECAE processing. However, the wear test results surprisingly showed that the ECAE process decreased the wear resistance of the alloy, although there was improvement in strength and ductility values. This was mainly attributed to the tribochemical reaction leading to oxidative wear with the abrasive effect in Al–Si alloys during sliding. The oxide layer played a dominant role in determining the wear resistance of the sample in both as-cast and ECAE-processed states, and it masked the effect of strengthening of alloy structure on the wear resistance.     

Achieving high strain rate superplasticity via severe plastic deformation processing

In this study, a thermomechanical process consisting of general precipitation and severe plastic deformation through equal channel angular extrusion (ECAE) was applied to a Zn-22 wt.% Al alloy to produce a microduplex structure for high strain rate (HSR) superplasticity studies. Microstructures, hardness, and superplastic properties of the Zn–Al alloy were studied by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), recordable hydraulic press, and a tensile test with a hot stage. A work-softening phenomenon due to the occurrence of a grain boundary-sensitive dynamic recrystallization (DRX) was observed during the ECAE processing of the Zn–Al alloy at the extrusion temperatures investigated from −10 °C to 50 °C. An important discovery regarding the grain boundary-sensitive DRV was realized in this study such that through a progressive work-softening process the Zn–Al alloy will eventually exhibit HSR superplastic properties.     

等径道角挤压对Mg-6Al合金性能的影响

为了优化铸态Mg-6Al合金等径道角挤压的工艺参数,通过等径道角挤压实验研究了工艺参数对其性能的影响.研究表明:等径道角挤压可大幅度提高Mg-6Al合金坯料的力学性能.当Mg-6Al合金挤压1道次至4道次后,其力学性能提高较大,微观组织明显细化.随挤压温度从260℃升高至300℃,被挤压坯料的力学性能先提高后降低.当挤压路径为路径B,挤压道次为4道次,挤压温度为300℃时,Mg-6Al合金的力学性能最高,其抗拉强度为308.2 MPa,延伸率达到30.6%.     

Microstructure and Properties of Al-6061 Alloy by Equal Channel Angular Extrusion for 16 Passes

The experimental researches on Equal Channel Angular Extrusion (ECAE) process of commercial available Al-6061 alloy were conducted and the grain refinement after ECAE processing was investigated. Sixteen passes of ECAE processing at room temperature were conducted and the relationship of grain refinement with extrusion pass was established. The property enhancements after ECAE processing including ultimate tensile strength and Vickers microhardness were investigated to determine the effects of the number of ECAE passes on the mechanical properties of the extruded samples. The research presents a whole picture of ECAE processing of the alloy for up to 16 passes.     

Effect of precipitates on damping capacity and mechanical properties of Ti–6Al–4V alloy

The present study was concerned with the effects of over-aging on damping property and fracture toughness in Ti–6Al–4V alloy. Damping property and toughness become important factors for titanium implants, which have big modulus difference between bone and implant, and need high damping capacity for bone-implant compatability. Widmanstätten, equiaxed, and bimodal microstructures containing fine α₂ (Ti₃Al) particles were obtained by over-aging a Ti–6Al–4V alloy. Over-aging heat treatment was conducted for 200 h at 545 °C. Fracture toughness, Charpy impact, and bending vibration tests were conducted on the unaged and the over-aged six microstructures, respectively. Charpy absorption energy and apparent fracture toughness decreased as over-aging was done, even if the materials were strengthened by precipitation of very fine and strong α₂-Ti₃Al particles. On the other hand, damping properties were enhanced by over-aging in Widmanstätten and equiaxed microstructures, but was weakened in bimodal microstructure due to the softening of tempered martensite and the decreasing of elastic difference between tempered martensite and α phase contained α₂ particles, etc. These data can provide effective information to future work about internal damping and fracture properties of Ti–6Al–4V alloy.     

Tensile and impact-toughness behaviour of cryorolled Al 7075 alloy

The effects of cryorolling and optimum heat treatment (short annealing + ageing) on tensile and impact-toughness behaviour of Al 7075 alloy have been investigated in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic (liquid nitrogen) temperature and its mechanical properties were studied by using tensile testing, hardness, and Charpy impact testing. The microstructural characterization of the alloy was carried out by using field emission scanning electron microscopy (FE-SEM). The cryorolled Al alloy after 70% thickness reduction exhibits ultrafine grain structure as observed from its FE-SEM micrographs. It is observed that the yield strength and impact toughness of the cryorolled material up to 70% thickness reduction have increased by 108% and 60% respectively compared to the starting material. The improved tensile strength and impact toughness of the cryorolled Al alloy is due to grain refinement, grain fragments with high angle boundaries, and ultrafine grain formation by multiple cryorolling passes. Scanning electron microscopy (SEM) analysis of the fracture surfaces of impact testing carried out on the samples in the temperature range of −200 to 100 °C exhibits ductile to brittle transition. cryorolled samples were subjected to short annealing for 5 min at, 170 °C, and 150 °C followed by ageing at 140 °C and 120 °C for both 40% and 70% reduced samples. The combined effect of short annealing and ageing, improved the strength and ductility of cryorolled samples, which is due to precipitation hardening and subgrain coarsening mechanism respectively. On the otherhand, impact strength of the cryorolled Al alloy has decreased due to high strain rate involved during impact loading.     

Influence of equal channel angular extrusion processing parameters on the microstructure and mechanical properties of Mg–Al–Y–Zn alloy

An as-cast Mg–Al–Y–Zn alloy was successfully processed by equal channel angular extrusion (ECAE) in the temperature range of 225–400 °C, and the influences of processing temperature on the microstructure and mechanical properties were investigated. The use of back pressure during one-pass ECAE of Mg–Al–Y–Zn alloy was favorable for eliminating the undeformed area in the billet. At the processing temperature below 250 °C, the microstructures were characterized by unrecrystallised structure and the precipitated phase Mg₁₇Al₁₂ was elongated along the extrusion direction. With increasing processing temperature to 350 °C, a large number of recrystallised grains were obtained. Increasing processing temperature promoted workability but led to decrease in the strength of Mg–Al–Y–Zn alloy. Then billets of as-cast Mg–Al–Y–Zn alloy were extruded at different numbers of ECAE passes. It was found that the microstructure was effectively refined by ECAE and mechanical properties were improved with numbers of ECAE passes increasing from one-pass to four passes. However, strengths decreased slightly after five passes though the grain size decreased considerably.     

Microstructure and mechanical properties of SPD-processed an as-cast AZ91D+Y magnesium alloy by equal channel angular extrusion and multi-axial forging

The aim of this work is to study the microstructure and mechanical properties of an as-cast AZ91D+Y magnesium alloy processed via two different severe plastic deformation techniques, equal channel angular extrusion (ECAE) and multi-axial forging (MAF). The grains were significantly refined after only one pass for both ECAE and MAF processed billets. However, the homogeneity of the SPD-processed microstructure increased with increasing number of passes. Micro-hardness and tensile tests showed that billets processed by ECAE and MAF techniques followed a same behaviour. With the increase of the number of processing passes (accumulated strain), the values of micro-hardness, yield strength, ultimate tensile strength and elongation were observed to increase. Grain refinement caused by dynamic recrystallization was introduced to explain the effects of the number of processing passes (accumulated strain) on the microstructure and mechanical properties of AZ91D+Y magnesium alloys processed by ECAE and MAF techniques.     

等径道角挤压制备高力学性能细晶Mg-6Al合金

为了制备高力学性能细晶Mg-6Al合金坯料,采用金相显微镜、材料拉伸实验机等手段对Mg-6Al合金铸坯进行等径道角挤压实验研究.并利用热处理工艺对挤压后材料进行处理,研究热处理工艺参数对材料力学性能的影响规律.结果表明,Mg-6Al合金的铸坯的抗拉强度为196.4MPa,延伸率为12.6%.经过等径道角挤压的Mg-6Al合金坯料的晶粒被大大细化,其晶粒尺寸由铸坯的140μm左右细化到8μm左右.其力学性能有很大提高,抗拉强度由196.4MPa提高到308.2MPa;延伸率由12.6%提高到30.6%.等径道角挤压工艺是一种非常好的制备高力学性能、细晶Mg-6Al合金的工艺方法.固溶和人工时效热处理工艺对等径道角挤压的Mg-6Al合金坯料的强度有较大影响,对延伸率影响较小.     

Effects of equal channel angular pressing on the strength and toughness of Al–Cu alloys

Tensile and impact tests were performed on Al–0.63 wt%Cu and Al–3.9 wt%Cu alloys subjected to equal channel angular pressing (ECAP) with different number of passes. Besides the tensile properties, data about the static toughness and the impact toughness were obtained. The strength and the toughness of the Al–Cu alloys were ameliorated and upgraded to a high level collectively. In addition, fracture surface observations show that the fracture behavior of the Al–Cu alloys changes from brittle mode to ductile mode after multi-pass ECAP.     

多道次ECAE动态成型Al-Mg-Si合金导线组织与性能

借助S4800扫描电子显微镜、Philips DM420透射电子显微镜、SANS CMT5105电子万能材料试验机和QJ48双臂直流电桥,研究了多道次ECAE动态成型Al-Mg-Si合金导线的组织与性能。结果表明:4道次ECAE动态成型可制备平均尺寸在10μm左右甚至更小的Al-Mg-Si合金导线晶粒。随着Mg、Si含量的增加,合金导线的抗拉强度增大,伸长率与等效导电率降低。经160~170℃/7h时效处理后,Al-0.59%Mg-0.59%Si合金导线的抗拉强度、伸长率和等效导电率分别为305.71~309.63 MPa,4.7%~5.4%和55.18%IACS~56.33%IACS,与目前国产Al-Mg-Si合金导线(295 MPa,52.5%IACS)相比,导电性能显著提高。     

Microstructure and mechanical properties of Mg–Zn–Ca alloy processed by equal channel angular pressing

An ultrafine-grained (UFG) Mg–5.12 wt.% Zn–0.32 wt.% Ca alloy with an average grain size of 0.7 μm was produced by subjecting the as-extruded alloy to equal channel angular pressing (ECAP) for 4 passes at 250 °C. The fine secondary phase restricted the dynamic recrystallized (DRXed) grain growth during the ECAP processing, resulting in a remarkable grain refinement. A new texture was formed in the ECAPed Mg alloy with the {0 0 0 2} plane inclined at an angle of 58° relative to the extrusion direction. The yield stress (YS) was decreased in the as-ECAPed alloy with finer grains, indicating that the texture softening effect was dominant over the strengthening from grain refinement. The ductility of the as-ECAPed alloy was increased to 18.2%. The grain refinement caused an obvious decrease in work hardening rate in the as-ECAPed alloy during tensile deformation at room temperature.     

Effect of interlayer composition on the microstructure and strength of diffusion bonded Mg/Al joint

The diffusion bonding of Mg and Al alloys with different interlayer compositions was investigated, where the interlayer was prepared through hot dipping technique in pure Zn, Zn–8Al and Zn–5Al baths, respectively. By means of microstructure characterization and strength measurement, it is found that the interlayer obtained in Zn–5Al bath led to the formation of interface microstructure composed of mini Al-rich particles dispersed in MgZn₂ phase, this kind of phases constituent decreases the risk of embrittlement of entire diffusion bonding joint and benefits its mechanical performance greatly.     

Temperature dependence of impact toughness in Al–Li–Cu–Mg–Zr alloys

Abstract

The dependence on temperature of the impact toughness in Al–Li–Cu–Mg–Zr alloys was investigated focusing on the low temperature impact toughness. The impact toughness of Al–Li–Cu–Mg–Zr alloys in the low temperature region (≤ 423 K) increased with decreasing temperature. Laminated cracks, the number of which increased with the increase in impact toughness in the low temperature region, were observed and it was suggested that the appearance of these cracks resulted in part of the increase of the impact toughness of this alloy. The spectra of potassium and sodium were detected from the fracture surface of a specimen tested at room temperature. This indicates that a low melting point metal phase seems to affect the impact toughness near room temperature, i.e. this phase seems to produce the liquid metal embrittlement locally at the grain boundary.

MST/787     

The wetting of copper by Al–Zn–Sn solders

Copper wetting times were measured for various Al–Zn–Sn solders using a wetting balance. Wettability of Cu with the Al–Zn–Sn solders was enhanced by increasing the Al and Zn contents. A scanning electron microscope (SEM) investigation on the solidified wetting sample revealed that diffusion of Al and Zn towards Cu is responsible for the observed wetting behaviour. The dipping speed is also important.     

Study of the corrosion behavior of zinc and Zn–Co alloy electrodeposits obtained from alkaline bath using direct current

The corrosion behavior of Zn and Zn–Co alloy electrodeposits that were obtained from weakly alkaline glycine solutions has been studied. SEM, EDS and XRD were used to study surface morphology, chemical composition and phase structure of the coatings. Corrosion behavior of Zn and Zn–Co alloy coatings was studied by using potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. The results showed that increasing current density during deposition, increases cobalt content of the coating. It was also shown that increasing current density, up to 15 mA cm⁻², decreases the grain size and further increase in current density increases the grain size of the deposit. It was also noticed that corrosion resistance of deposits was highly influenced by the composition and morphology of the coatings. Zn–Co deposit containing 0.89 wt.% Co showed the highest corrosion resistance due to its single phase structure and its finer morphology.     

Thermal stability of the αZn–Mg2Zn11 and αZn–βAl eutectics obtained by Bridgman growth

The thermal stability of rod-like Zn–Mg2Zn11 and lamellar Zn–Al eutectics obtained by Bridgman growth of Zn–3.1 wt% Mg and Zn–5 wt% Al has been studied for soaking times up to 10 h at 300 and 350°C, respectively. Two-dimensional coarsening resulted for Zn–Mg2Zn11 grown at 0.5 and 1 mm s-1 while fault migration was operative for lamellar Zn–Al grown at 0.1 and 1 mm s-1. Hardness decreased with increased soaking time according to a Hall–Petch relationship with mean interphase spacing and the values H0 and kY accord well with the values obtained from the Hall–Petch relationship for HV of as-solidified Zn–Mg2Zn11 and Zn–Al with eutectic interphase spacing, respectively. © 1998 Chapman & Hall     

Mechanical behaviour of Zn–Fe alloy coated mild steel

Zinc alloy coatings containing various amounts of Fe were deposited by electrodeposition technique on a mild steel substrate. The concentration of Fe in the produced alloy coatings ranged from 0 to 14 wt.%, whereas the thickness of the coatings was about 50 μm. Structural and metallurgical characterization of the produced coatings was performed with the aid of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques. This study aims in investigating the mechanical behaviour of Zn–Fe coated mild steel specimens, as no research investigation concerning the tensile behaviour of Zn alloy coated ferrous alloys has been reported in the past. The experimental results indicated that the ultimate tensile strength of the Zn–Fe coated mild steel was lower than the bare mild steel. In addition, the ductility of the Zn–Fe coated mild steel was found to decrease significantly with increasing Fe content in the coating.     

Dynamic mechanical properties of a near-nano aluminum alloy processed by equal-channel-angular-extrusion

Microstructure of AA5056 AlMg alloy is refined drastically to nano-scale by the equal-channel-angular-extrusion(ECAE) process. Dynamic mechanical properties at room temperature in the ECAE processed 5056 AlMg alloy (5056-ECAE) are characterized by a modified Hopldnson-bar method. Yield stress (YS) in 5056-ECAE exhibits remarkably higher value than that of a fully annealed 5056 alloy(5056-0). Hall-Petch(H-P) relation of 5056 alloy is compared with those of a binary AlMg alloy and Aluminum. The slope of the H-P relation in the granular 5056 alloy is almost equal to that of a binary AlMg alloy with a similar content of magnesium, and larger than that of Aluminum. On the other hand, the slope of the sub-grained alloy exhibits lower value than that of the granular alloy. The result indicates that grains effectively refined by the ECAE process, however, the grain boundary strength of the sub-grained alloy is relatively lower than that of the granular alloy. The elongation-to-failure of 5056-ECAE exhibits a larger value than those of some fine-grained bulk aluminum alloys such as a mechanically alloyed aluminum. Fractography of 5056-ECAE revealed that this alloy was fractured with ductile dimples. The result supports the possibility that this alloy exhibits the high speed impact performance and capability for high-rate forming.     

Effect of grain refining and Sr-modification interactions on the impact toughness of Al–Si–Mg cast alloys

The present work investigates the effects of various types of grain refiners on the impact properties of Sr-modified A356.2 alloys in both the as-cast and heated-treated conditions. The results showed that the addition of Ti and B greatly improves the alloy toughness, but only when the alloy was in a fully modified state; moreover, the right type of master alloy and addition levels must be used. The highest values of the total absorbed energy recorded for T6-tempered alloys were obtained using Al–5%Ti–1%B and Al–10%Ti master alloys in addition to 0.04%Ti. A significant deterioration in the impact properties is observed due to the Sr–B interaction (in some cases). The improvements in toughness may be attributed to the change in Si particle morphology as well as to the dissolution and fragmentation of a number of the intermetallics formed during the T6 temper.