Microstructure and mechanical properties of Mg–6Sn and Mg–6Zn alloys prepared by different processing techniques: a comparative study

The microstructure and mechanical properties of Mg–6Sn and Mg–6Zn are investigated and compared in cast/heat treated, rolled and extruded conditions. Compared to the heat treated alloys, the grain size of both alloys decreases while the volume fraction of precipitates increases by rolling and extrusion in Mg–6Sn alloy at 350 ºC due to dynamic recrystallization and dynamic precipitation of intermetallic phases. Zinc has a stronger grain refining effect than tin in the heat treated alloys while the opposite effect is found in the rolled and extruded alloys. For the heat treated alloys the Mg–6Sn the strength reached 158.7 MPa with elongation 5.2% while Mg–6Zn exhibited a higher strength of 183.7 MPa and 8.4% elongation. In rolled condition the strength of Mg–6Sn reached 224 MPa with 1.6% elongation while Mg–6Zn exhibited a lower strength of 124 MPa and a lower ductility of 0.5% elongation due to susceptibility to hot shortness. Extrusion of Mg–6Sn alloy resulted in the maximum attained strength of 281 MPa and an elongation of 6.1% while Mg–6Zn cracked during extrusion due to hot shortness. The results obtained are discussed with respect to microstructure evolution in both alloys.     

Effect of boron on microstructure and mechanical properties of eutectic aluminum‐silicon alloy modified with phosphorus

In order to understand the effect of boron on the microstructure and mechanical properties of eutectic aluminum‐silicon alloy modified with phosphorus, complex modification of eutectic aluminum‐silicon alloy by aluminum‐3phosphorus and aluminum‐3boron was conducted. The results show that the area fraction of primary α‐aluminum in eutectic aluminum‐silicon alloy modified with aluminum‐3phosphorus increased first and then decreased with increasing amounts of aluminum‐3boron. The area fraction and the size of primary silicon decreased rapidly first and then stabilized. The morphology of eutectic silicon transformed from needle‐like into fine short rods or granules after complex modification with aluminum‐3phosphorus and aluminum‐3boron. The ultimate tensile strength of the alloy modified with 0.4 wt.% aluminum‐3phosphorus and 0.2 wt.% aluminum‐3boron increased by 18 %, compared with that of the eutectic aluminum‐silicon alloy modified with aluminum‐3phosphorus, while the elongation decreased by 5 %. It was concluded that the comprehensive mechanical properties of eutectic aluminum‐silicon alloy were improved.     

Comparative experimental study on the modification of microstructural and mechanical properties of friction stir welded and gas metal arc welded EN AW‐6061 O aluminum alloys by post‐weld heat treatment

In this paper, the effects of post‐weld heat treatment on modification of microstructures and mechanical properties of friction stir welded and gas metal arc welded AA6061‐O plates were compared with each other. Gas metal arc welding and friction stir welding were used as the applicable welding processes for AA6061‐O alloys. The applied post‐weld heat treatment consisted of solution heat treatment, followed by water quenching and finally artificial aging. The samples were classified as post‐weld heat treated and as‐welded joints. The microstructural evolution, tensile properties, hardness features and fracture surfaces of both as‐welded and post‐weld heat treated samples were reported. The results clearly showed that friction stir welding process demonstrated better and more consistent mechanical properties by comparison with the gas metal arc welding process. The weld region of as‐welded samples exhibited a higher hardness value of 80 HV0.1 compared to the base material. In addition, the feasibility of post‐weld heat treatment in order to enhance the mechanical properties and to obtain more homogeneous microstructure of 6061‐O aluminum alloys was evaluated.     

Influence of microstructure on fatigue crack propagation under bending in the alloy Ti–6Al–4V after heat treatment

The paper presents the test results obtained for fatigue crack growth in Ti–6Al–4V titanium alloy subjected to bending. The tests were performed in plane specimens with the stress concentrators being a one‐sided sharp notch. The tested specimens were made of the oxygenated Ti–6Al–4V subjected to various variants of heat treatment. The tests were carried out at the fatigue test stand MZGS‐100 under loading frequency 28.4 Hz. From the obtained results of fatigue and structural tests it appears that schemes of crack propagation and fatigue lives of the considered alloy are different depending on a structure obtained as a result of a given heat treatment.     

The effect of the solution treatment onto the microstructure and mechanical properties of MAG pulsed welded joints from X2CrNiMoN22‐5‐3 Duplex stainless steels

The metallurgical behaviour by Duplex stainless steels welding is affected by reducing the austenite proportion in weld and in the area adjacent to the fusion line of the molten metal bath and also by the precipitation of nitrides Cr₂N, carbides M₂₃C₆ and intermetallic phases, σ, χ, Laves. The modalities for obtaining a quantitative ratio of the two phases (Austenite/Ferrite) close to that of the base metal (～50 % Austenite and 50 % Ferrite) aims to adjust the chemical composition of the weld by selecting a filler material with a higher nickel content (the element which beside nitrogen promotes the austenite formation), the heat cycle control of the welding process and the application of a post‐welding solution treatment. The present paper explores the effect of such heat treatment on balance restoring between austenite and ferrite and the reduction of the alloying elements segregation phenomena. By optical and scanning electron microscopy examinations and also X‐ray diffraction analyses the microstructural changes induced by the applied treatment are highlighted and by impact toughness and static tensile tests is demonstrated the positive effect of the heat treatment onto the ensuring of the welded joints quality.     

Microstructure and mechanical properties of an Al‐Si alloy reinforced by Al64Cu24Fe12 quasi‐crystalline particles

In this work, aluminum‐silicon alloy reinforced with Al₆₄Cu₂₄Fe₁₂ quasi‐crystalline particles have been prepared by a traditional casting method with proper heat treatment process. The microstructures of the composites were examined using optical microscopy, scanning, X‐ray and energy dispersive spectrometer. The results indicate that there was no quasi‐crystalline phase remained and a new phase‐β (Al_65‐75Si_13‐26Fe_3‐10) phase formed, which may act as a new reinforcing phase. There are three primary phases in the final composite: eutectic silicon, β‐phase and the α‐aluminum phase. Also the changes of mechanical properties were studied by tensile test and Vickers hardness test. The test results demonstrate that the mechanical properties of the composite is remarkably improved by adding proper amount of quasi‐crystalline particles. After adding 7.70 vol.% quasi‐crystalline particles, the tensile strength and the hardness increased by 70 % and 62 % respectively. However, adding a big amount (10.09 vol.%) of particles to molten aluminum‐silicon alloy will cause the particles aggregation and adhesion, which resulted in the decrease of the mechanical properties.     

Influence of process chains on heat treatment

The results of a heat treatment are influenced by the state of the material before heat treatment, e. g. microstructure, residual stresses, surface layers, etc. Consequently, different production chains can lead to differences in microstructure and distortion behavior. In this case properties as well as time and costs of hard machining after heat treatment are influenced. This paper was first published in German in HTM Journal of Heat Treatment and Materials ©Carl Hanser Verlag, Muenchen/Germany and gives examples for the influences of production chains on thermochemical treatments such as case hardening [1].     

Processing and properties of a new biodegradable Mg−Zn−Ca−Zr alloy

Magnesium alloys are used for degradable orthopaedic and cardiovascular implants due to their favourable mechanical and biological properties, degradation ability in physiological environment and stimulatory effect on the new bone formation. The research challenges are related to the increase of biological and mechanical compatibility. For the present study, a magnesium based alloy design was conducted to the following chemical composition: Mg?2.7Zn?1Ca?0.6Zr (wt.%). A complex thermomechanical processing route was applied: a plastic deformation by extrusion at various temperatures and deformation degrees (400 °C–480 °C, ? = 20 %–40 %), followed by various final heat treatments at 200 °C–400 °C for 10 min–60 min. Further, the influence of processing parameters upon the structure, mechanical properties and biological response was studied. Processed specimens were characterized by scanning electron microscopy (secondary electron imaging and energy dispersive spectroscopy) and mechanically by tensile tests. The most representative results were obtained for the samples extruded at 450 °C/? = 20 %, followed by a final heat treatment at 350 °C/15 min, air cooling. Further, for samples which revealed promising results, in‐vitro testing was developed. Biocompatibility testing of the Mg?2.7Zn?1Ca?0.6Zr (wt.%) alloy was realized by indirect contact studies using the Vero (ATCC® CCL‐81?, American Type Culture Collection) cell line. Cells morphologies, cell viability and proliferation were evaluated.     

热处理对BT14钛合金显微组织和力学性能的影响

本文研究了BT14钛合金热处理规范→显微组织→力学性能之间的关系.结果表明:热处理工艺对组织和力学性能的影响很大.其中,随着退火温度的升高,初生α相含量逐渐减小,α相颗粒逐渐粗化,向等轴状发展;随着退火温度的升高,合金的强度和硬度逐渐减小,但塑性变化是先升高后减小的趋势.热处理强化规范中低温淬火 低温时效所得的合金综合性能较优.但BT14钛合金强化效果不明显.     

Friction stir welding of thick section Al‐Zn‐Mg‐Cu aluminum alloy

Friction stir butt welding of 25 mm thick AA7075–T651 plates has been investigated. Careful process parameter selection resulted in single pass, full‐penetration defect free welds. The weld nugget exhibits a significant grain refinement while facing the dissolution of strengthening precipitates. Microhardness survey gives a W‐shaped profile with lower hardness values recorded in the thermo‐mechanically‐affected zone. Tensile fractures occur, again, in the thermo‐mechanically‐affected zone, where minimum hardness occurred. The friction stir welds demonstrate an excellent root bend performance while falling behind base material in face bend test. The welds also displayed outstanding impact toughness compared to that of parent material. It is concluded that defect free single pass friction stir welds can be successfully made on 25 mm thick AA7075–T651 plates.     

Enhancement of work‐hardening behavior of dual phase steel by heat treatment

The work‐hardening response and mechanical properties of dual phase steels originated from different initial microstructures under low and high martensite volume fractions were investigated using a typical carbon‐manganese steel. The modified Crussard‐Jaoul analysis was used for studying the work‐hardening stages and the deformation behavior of ferrite and martensite. It was revealed that the initial martensitic microstructure before intercritical annealing is much better than the full annealed banded ferritic‐pearlitic and spheroidized microstructures in terms of work‐hardening capacity and strength‐ductility trade off. By increasing the amount of martensite, via intercritical annealing at higher temperatures, the ductility decreased but the tensile toughness of dual phase steels increased toward reaching the domain of extra‐advanced high‐strength steels due to the enhancement of work‐hardening rate.     

Mikrostrukturelle Pressschweißnahtcharakterisierung im strangpressten Zustand für Al‐Mg‐Si‐Legierungen

Weld seams form when profiles are extruded using porthole or bridge dies. These are inevitable when producing industrial relevant hollow profiles but imply the weak spot if the profiles are used for applications with high mechanical requirements. The characterization of formed weld seams together with their mechanical properties is problematic or sometimes even impossible due to the complex profile geometries. Expansion, bending or tensile tests of profiles or parts of the same were hitherto often used for their analysis lacking the possibility of basic assumptions about their properties. The investigations described herein circumvent the problem by using a flat profile exhibiting the weld seam in the middle. Flat profiles offer the possibility of standardised specimens for tensile testing. The extrusion experiments focused on the aluminium alloys EN‐AW 6060 and EN‐AW 6082. During the experiments billet temperature and extrusion speed have been varied. The microstructure was analysed subsequent to explain the obtained results and to offer a possibility of characterisation.     

Comparison of the mechanical and microstructural properties of heat‐treated boron steel in different cooling media

This paper focuses on the effects of heat treatment parameters on the microstructural and mechanical properties of quenchable 30MnB5 steel. Heat treatment parameters, such as different cooling media and different heating times at the same temperature, were investigated and compared. Tensile and hardness tests were performed at room temperature, and then the microstructures of the specimens were studied using optical microscopy and the results were compared. The results showed that boron steel heat treated using a water quenching process exhibited the best mechanical properties because of the formation of a martensitic microstructure.     

热处理对铸造Ti15-3合金显微组织和力学性能的影响

借助光学显微分析、ＴＥＭ和ＳＥＭ分析手段研究了不同热处理工艺对Ｔｉ１５－３合金显微组织和力学性能的影响。结果表明：合金在铸态时的组织特征为粗大的β相,由于合金中没有析出相的弥散强化作用,因而合金的强度低,在不同温度时效处理后,在晶内和晶界析出α相,随着时效温度和时效时间的增加,析出相不断粗化,与铸态相比,合金时效后强度大幅度提高而处伸率大幅度下降,在变形过程中,合金中的位错在析出相周围形成缠结,合     

Dependence of the mechanical properties and microstructure of ultralight magnesium-lithium-aluminum alloy on heat treatment conditions

Although magnesium-lithium-based alloys demonstrate superior workability and lower densities than conventional magnesium alloys, their mechanical properties require improvement. In this study, the effect of heat treatment conditions on the mechanical properties and microstructure of magnesium-lithium-aluminum alloys was investigated. Tensile tests were conducted on the alloys, and the results showed that the yield stress, ultimate tensile strength, and total elongation were significantly dependent on the heat treatment conditions. The relationship between the yield stress and grain size was not governed by the Hall-Petch relationship. The activation volume of various heat-treated samples estimated from the strain rate jump test was smaller for higher yield stress. Wide-angle x-ray scattering indicated that the second phase with a Bragg spacing of 1.7 nm was generated after heat treatment. It is found that the state of the second phase periodic structure affects the mechanical properties of the magnesium-lithium-aluminum alloy.     

The influence of post‐heat treatments on the tensile strength and surface hardness of selectively laser‐melted AlSi10Mg

To improve the mechanical properties of cast aluminium alloys several post‐heat treatments are known. However, these treatments cannot directly be transposed to additively via selective laser melting manufactured aluminium alloys, e. g., aluminium‐silicon‐magnesium (AlSi10Mg). Therefore, this study aims to determine suitable post‐heat treatments to optimise the mechanical properties of SLM‐built AlSi10Mg specimen. The influence of various post‐heat treatment conditions on the material characteristics was examined through hardness and tensile tests. The findings indicate that the Vickers hardness and ultimate tensile strength could not be improved via secondary precipitation hardening, whereas the fracture elongation shows a value which is distinctly higher than the values of a comparable cast alloy. Solution annealing at 525 °C reduces the hardness and the ultimate tensile strength by about 40 % and increases the fracture elongation three times. A subsequent precipitation hardening allows recovery of 80 % of the as‐built hardness, and 90 % of the previous ultimate tensile strength combined with maintaining an improved fracture elongation of about 35 % compared to the respective as‐fabricated condition.     

热处理对Ti35Nb3.7Zr1.3Mo合金的组织与性能影响

依据钛合金相关设计理论设计了低弹性模量、中高强度、良好塑性的新型生物医用近β型Ti35Nb3.7Zr1.3Mo合金,研究了固溶温度和时效温度对合金组织和力学性能的影响。结果表明:随着固溶温度的升高,α相逐渐溶解,合金的强度和弹性模量尚未发生明显变化。在低温时效时析出脆性ω相;随着时效温度升高,逐渐析出α相,且α相逐渐粗化;合金的强度与弹性模量先升高,达到峰值后下降;延伸率先降低后升高。合金经750℃固溶和450℃时效后综合力学性能优良,可以满足生物植入材料力学性能的要求。     

Effect of the heat treatment on the microstructure and mechanical properties of medium-Mn-steels

ABSTRACT

The heat-treatment (HT) schedule and selected annealing parameters have a substantial effect on the microstructure and mechanical properties of medium-Mn-steels. The structure morphology depends on the fact, whether the austenite-reverted transformation takes place from deformed (one-step HT) or non-deformed (two-step HT) microstructures. Depending on the intercritical annealing temperature, the stability of the retained austenite can be altered to a large extent. As a result, the mechanical properties can be adjusted from high strength with excellent ductility to very high strength with reasonable ductility. The present contribution, therefore, elucidates the dependence of the microstructural characteristics and material behaviour on the HT parameters for medium-Mn alloy compositions with different Mn-contents.

This paper is part of a Thematic Issue on Medium Manganese Steels.     

热处理对电沉积Ni-Fe合金箔组织和力学性能的影响

电沉积法制备Ni-Fe合金箔具有工艺简单,能耗低,产品规格不受限制等优点,但其塑性和弹性模量较低限制了其应用发展.为了改善电沉积Ni-Fe合金箔的力学性能并扩大其应用范围,本文通过高温热处理方法改善其力学性能,采用SEM,XRD,EBSD分析手段对电沉积Ni-Fe合金箔晶粒组织和结构进行了分析,通过高温热台显微镜进行原位在线观测晶粒组织的演变过程,并对热处理后的电沉积Ni-Fe合金箔进行力学性能分析.研究表明,热处理过程中电沉积Ni-Fe合金箔经历细晶组织阶段、混晶组织阶段和粗晶组织阶段,其中,在1 000~1 050℃容易发生晶粒异常长大.细晶组织阶段,电沉积Ni-Fe合金箔能够保证较高的强度,且塑性和弹性模量明显提高,综合性能较好;混晶组织阶段,强度和塑性较低,弹性模量有一定程度提高;粗晶组织阶段,强度很低,但塑性和弹性模量有较大程度提高.     

Effect of heat treatment on the corrosion resistance and mechanical properties of selective laser melting Ti6Al4V alloy

The present work shows that the effect of several heat treatments on the corrosion resistance and mechanical properties of Ti6Al4V processed by selective laser melting (SLM). The microstructure of Ti6Al4V alloy produced by selective laser melting exhibited bulky prior β columnar grains, and a large amount of fine acicular martensites α′ were observed inside the prior β columnar grains. The acicular martensitic α′ were transformed to a mixture of α and β after heat treatment, and the grain size increases with the increase of heat-treated temperature. The results of 3.5 wt% NaCl solution electrochemical corrosion test showed that the heat-treated samples possess a higher corrosion resistance than the as-received sample. Among of them, the sample after heat-treated at 730 °C exhibited best corrosion resistance and excellent fracture strain. The sample heat treated at 1015 °C showed worst mechanical properties due to the formation of Widmanstätten structure.