Formability of continuous cast 5052 alloy thin sheets

The formability of continuous cast 5052 alloy thin sheets from two different process schedules was examined. One was prepared in the laboratory by cold-rolling from a continuous cast thick plate followed by annealing (lab-processed sheet), and the other was produced by a new process involving hot-rolling followed immediately by in-line annealing (in-line annealed sheet). Tensile test results indicate that all the lab-processed sheets exhibit evident yield behavior. Increasing rolling reduction results in an increase of strength and a decrease of ductility in the lab-processed sheets due to increasing contribution of centerline segregation of second-phase particles. Both the lab-processed sheets annealed at 400 °C for 90 min and the in-line annealed sheets exhibit tensile elongation of more than 20% and two-stage strain hardening behavior. Compared with the lab-processed sheets, the in-line annealed sheet annealed at 454 °C has higher values of UTS and elongation. Furthermore, forming limit curves were determined. It is found that the level of the forming limit curve of the lab-processed thin sheet is lower than that of conventionally produced 5052-O Al, but close to that of 6111-T4 Al sheet. Moreover, the in-line annealed sheets have higher limit strains than the lab-processed sheets. These results demonstrate that the in-line annealing process results in the production of continuous cast alloy sheet with improved formability.     

Effect of high temperature annealing and subsequent hot rolling on microstructural evolution at the bond-interface of Al/Mg/Al alloy laminated composites

Using a two-pass hot rolling process, Al(5052)/Mg(AZ31)/Al(5052) alloy laminated composite plates were fabricated. The first pass was performed at relatively low temperatures, and the second pass was performed at higher temperatures. No new phases formed at the bond interface after the first hot rolling pass. High temperature annealing with the annealing temperature at or above 300 °C caused the formation of continuous layers of the intermetallics Mg17Al12 and Al3Mg2 at the bond interface of Al(5052)/Mg(AZ31). The growth rate of the intermetallic layers increased with increasing the annealing temperature, while the incubation time decreased with increasing the temperature. A kinetic equation was developed to describe the growth of the intermetallic compound layers. The second hot rolling pass caused the break of the continuous intermetallic layers into fragments, which were intermittently dispersed at the bond interface.     

Mechanical behaviour and texture of annealed AZ31 Mg alloy deformed by ECAP

Abstract

AZ31 Mg alloy samples were processed by equal channel angular pressing (ECAP) at 220°C for four passes. An average grain size of ～1·9 μm with reasonable homogeneity was obtained. The ECAP process imparted large plastic shear strains and strong deformation textures to the material. Subsequent annealing of the equal channel angular pressed samples produced interesting mechanical behaviours. While yield strength increased and ductility decreased immediately after undergoing ECAP, annealing at temperatures <250°C restored ductility significantly at a small decrease in of yield strength. Annealing at temperatures >250°C reduced yield strength without additional improvement in ductility. It is believed that the combination of stress relief via dislocation elimination, refined microstructure and the retention of a strong ECAP texture at low annealing temperatures enhance ductility. High temperature annealing breaks down the ECAP texture resulting in no further improvement in ductility. The results show that the mechanical properties of the alloy can be positively influenced by annealing after ECAP to achieve a combination of strength and ductility.     

Enhanced tensile ductility in a nanostructured Al–7·5%Mg alloy

Abstract

This paper reports work on the enhanced tensile ductility in a nanostructured Al–7·5%Mg alloy with a mean grain size of 90 nm processed via consolidation of cryomilled Al–Mg powders. An annealing treatment at a temperature of 773 K for 2·5 h modified the extruded microstructure slightly without causing significant grain growth, as revealed by TEM and XRD patterns. The annealing treatment significantly improved the ductility, with a remarkably small loss in strength. The observed high thermal stability of the cryomilled Al alloy was attributed to the existence of impurity elements introduced during cryomilling and the presence of a supersaturated solid solution. The reported phenomenon of enhanced tensile ductility was attributed to a mechanism involving dislocation activity in submicron grains during plastic deformation.     

The effect of friction stir processing on the microstructure and mechanical properties of equal channel angular pressed 5052Al alloy sheet

In this study, equal channel angular pressed (ECAP) 5052Al alloy sheet was friction stir processed (FSP). This was carried out to understand the effect of FSP on the microstructure and mechanical properties of the ECAP sheet. FSP led to further grain refinement and a tighter distribution of grains. Fraction of high-angle grain boundaries changed from 15% in ECAP condition to more than 70% after FSP. Although FSP caused lowering of yield strength (YS) and ultimate tensile strength (UTS), it resulted into a substantial improvement in uniform deformation region of the tensile sample (from 1.3% in as-received condition to 12.9% in FSP condition). Strain hardening rate (SHR) analysis showed lowering of recovery rate on FSP. A static grain growth model correctly predicted the average grain size obtained after FSP. Existing grain boundary, solid solution, and dislocation strengthening models were used to estimate the YS of 5052Al alloy in both the conditions. The strengthening model was able to predict the YS of the alloy in as-received and FSP conditions very well.     

A nanostructural design to produce high ductility of high volume fraction SiCp/Al composites with enhanced strength

High ductility and increased strength of SiC_p/Al composites are highly desirable for their applications in complicated components. However, high ductility and high strength are mutually exclusive in high volume fraction SiC_p/Al composites. Here, we report a novel nanostructuring strategy that achieves SiC_p/Al–Sc–Zr composites with superior maximum tensile strain and enhanced tensile strength. The new strategy is based on combination of grain refinement down to ultra-fine scale with nanometric particles inside the grain through adding distinctive elements (Sc, Zr) and refining nucleation centers to nanoscale under the action of high volume fraction reinforcement during the fabrication process. The nanostructured SiC_p/Al–Sc–Zr composites had an increase of ∼300% in maximum tensile strain and a 21% increase in tensile strength. This thought provides a new sight into enhancement of both strength and ductility of particle reinforcement metal matrix composites.     

钛铝合金板材压印成形及接头力学性能实验研究

对钛合金(TA1)和铝合金(Al5052)板材组合进行压印连接的可行性进行了研究,发现压印连接可以有效地实现TA1-TA1组合和Al5052-TA1组合的连接。对所获得的接头进行准静态力学性能测试,并运用扫描电子显微镜对接头拉伸断口进行微观分析。结果表明,压印连接时,钛合金和铝合金的组合能够获得成形性较好的压印接头,TA1-TA1接头的最大载荷和失效位移较Al5052-TA1接头提高了303.8%和49.4%,这两种接头静态失效形式相似,为上板颈部材料首先被破坏,产生裂纹,之后裂纹沿周向逐渐扩展,最终导致整个压印接头断裂。由微观断口可以判断TAl-TA1接头断口处呈现准解理和韧窝形貌,即同时具有韧性断裂和脆性断裂的特征;Al5052-TA1接头断口处呈现直径和深度较大的拉长韧窝,即为韧性断裂。     

Mechanical Alloying of Ti50Al50 Powders and Their Consolidated Properties

Elemental powder mixtures of 50Ti-50Al (at.%) were mechanically alloyed via various ball milling methods. The microstructural evolution during the milling indicates that the mechanical alloying behavior is strongly affected by milling methods, and horizontal ball milling is most effective for producing homogeneous metastable powders. The mechanically alloyed powders were consolidated by vacuum hot pressing followed by homogeneous annealing. Compression testing results showed that the annealed specimens still retain fine grains and have a good combination of fracture strength and ductility, as compared to cast specimens of the same alloy.     

A medium manganese steel designed for water quenching and partitioning

An aluminium-containing medium manganese steel has been designed to undergo intercritical annealing followed by quenching in water and subsequent partitioning. Water quenching, replacing the quenching temperature (QT) between 150 and 300°C in conventional quenching and partitioning steels, is therefore adopted in QP alloys, in order to guarantee the precise QT in practice. The low intercritical annealing temperature of 750°C refines both ferrite and prior austenite grains into submicron size. The large fraction of ultra-fine ferrite, as well as the transformation-induced plasticity effect of retained austenite, improves the overall ductility of this water-quenched and partitioned steel. The alloy has achieved excellent mechanical properties of 1130?MPa ultimate tensile strength combined with 19.2% total elongation.     

Nanoscale deformation of multiaxially forged ultrafine-grained Mg-2Zn-2Gd alloy with high strength-high ductility combination and comparison with the coarse-grained counterpart

Cold processing of magnesium(Mg) alloys is a challenge because Mg has a hexagonal close-packed(HCP)lattice with limited slip systems, which makes it difficult to plastically deform at low temperature. To address this challenge, a combination of annealing of as-cast alloy and multi-axial forging was adopted to obtain isotropic ultrafine-grained(UFG) structure in a lean Mg-2Zn-2Gd alloy with high strength(yield strength: ~227 MPa)-high ductility(% elongation: ~30%) combination. This combination of strength and ductility is excellent for the lean alloy, enabling an understanding of deformation processes in a formable high strength Mg-rare earth alloy. The nanoscale deformation behavior was studied via nanoindentation and electron microscopy, and the behavior was compared with its low strength(yield strength: ~46 MPa)-low ductility(% elongation: ~7%) coarse-grained(CG) counterpart. In the UFG alloy, extensive dislocation slip was an active deformation mechanism, while in the CG alloy, mechanical twinning occurred.The differences in the deformation mechanisms of UFG and CG alloys were reflected in the discrete burst in the load-displacement plots. The deformation of Mg-2Zn-2Gd alloys was significantly influenced by the grain structure, such that there was change in the deformation mechanism from dislocation slip(non-basal slip) to nanoscale twins in the CG structure. The high plasticity of UFG Mg alloy involved high dislocation activity and change in activation volume.     

ODS ferritic steel engineered with bimodal grain size for high strength and ductility

An attractive way to enhance the ductility of ODS ferritic steels is to develop an alloy with a bimodal grain size distribution, in which the micron-sized coarse grains provide high ductility. The nanometer-sized fine grains enhance the tensile strength. The microstructures were obtained by blending the gas-atomized powders and mechanical alloyed powders, followed by hot forging and annealing. The homogeneously distributed nanometer-sized oxide nanoparticles can also be detected. Mechanical properties tests revealed a great improvement in ductility in comparison with other ODS ferritic steels, and high strength over the whole range of test temperatures, owing to the fine grains and oxide nanoparticles. The combination of high ductility and high strength makes this ODS ferritic steel much promising in high-temperature application.     

Effect of rolling temperature on microstructure and mechanical properties of 6063 Al alloy

Aluminium alloy (6063) was severely rolled upto 92% thickness reduction at liquid nitrogen temperature and room temperature to study the effect of rolling temperature on its mechanical properties and microstructural characteristics by using tensile tests and SEM/electron back scattered diffraction (EBSD), transmission electron microscope (TEM), DSC, X-ray diffraction (XRD) as compared to room temperature rolled (RTR) material with the same deformation strain. An improved strength (257 MPa) of cryorolled 6063 Al alloy was observed as compared to the room temperature rolled alloy (232 MPa). The improved strength of cryorolled alloy is due to the accumulation of higher dislocation density than the room temperature rolled material. The tensile properties of cryorolled alloy and the alloy subjected to different annealing treatments were measured. The cryorolled alloy subjected to annealing treatment at 300 °C for 5 min exhibits an ultrafine-grained (UFG) microstructure with improved tensile strength and ductility.     

Enhancing electrical conductivity and strength in Al alloys by modification of conventional thermo-mechanical process

Although aluminum alloys can be made as excellent conductors, their applications to electrical and electronic industries are often limited because of their relatively low strength. A new strategy of micro-structural design for improving combination of electrical conductivity and strength in Al alloy is developed based on modification of the sequence of conventional cold-deformation and artificial aging. The proposed thermo-mechanical process could enhance the removal of solutes from the Al matrix and properly utilize the work-hardening effect to compensate the loss of age-hardening effect due to the coarsening of the hardening precipitates in the material, such that an excellent combination of good electrical conductivity and enhanced strength as well as reasonable ductility can be achieved in an Al–Mg–Si–(Cu) alloy. The featured microstructure of the alloy was examined in order to understand the obtained properties of the material.     

Microstructural Evolution and Thermal Stability of Ultra-fine Grained Al-4Mg Alloy by Equal Channel Angular Pressing

Experiments were conducted to evaluate the grain refinement and thermal stability of ultra-fine grained Al-4Mgalloy introduced by equal-channel angular pressing (ECAP) at 473 K. The results show that the intensities of X-ray(111/222) and (200/400) peaks for the alloy processed by ECAP decrease significantly and the peak widths of halfheight become broadening compared with the corresponding value in the annealed alloy. The microstructure of 2passes ECAPed alloy consists of both elongated and equiaxed subgrains. The residual strain in the alloy increaseswith increasing passes numbers, that appears as increasing dislocation density and lattice constant of matrix. Anequiaxed ultra-fine grained structure of～0.2μm is obtained in the present alloy after 8 passes. The ultra-fine grainsare stable below 523 K, because the alloy retains extremely fine grain size of～1μm after static annealing at 523 Kfor 1 h.     

Controllable fabrication of a carbide-containing FeCoCrNiMn high-entropy alloy: microstructure and mechanical properties

Previous studies have reported that high carbon contents in FeCoCrNiMn high-entropy alloys lead to carbides precipitating from the alloys. Typically, carbides are used to improve the strength of alloys but also lead to decreased ductility. However, the strength and ductility of alloys can be improved when carbides shape, size and distribution are carefully controlled. Therefore, a carbide-containing FeCoCrNiMn alloy with 2?at.-% carbon was prepared by arc melting, and its microstructure and mechanical properties were further tuned by cold rolling with subsequent annealing treatment. The yield strength and uniform elongation of the resultant alloy were excellent, reaching 581?MPa and 25%, respectively, due to the additive combination of various strengthening mechanisms, such as solid-solution hardening, grain-boundary hardening and precipitation hardening.     

Effect of cryo groove rolling followed by warm rolling (CGW) on the mechanical properties of 5052 Al alloy

The influence of cryo groove rolling followed by warm rolling (CGW) on the mechanical behavior of AA 5052 has been investigated in the present study. The solution-treated (ST) Al alloys were subjected to cryo groove rolling (CGR) followed by warm rolling to a true strain of 2.3 at different temperatures. The CGR samples rolled at 175°C show improved strength (328?MPa) and hardness (131 Hv) with 4.1% ductility, as compared to the ST alloy. It was due to the formation of a duplex microstructure consisting of both elongated and equiaxed sub-grains. Apart from this, the formation of fine precipitates along with deformed or broken impurity phase particles is also responsible for enhancement in the tensile strength of CGW samples. Furthermore, the deformed (CGW) material was subjected to post-annealing treatment between temperatures of 180 and 300°C for one hour to study its effect on the mechanical behavior of the alloy. The post-deformation annealed samples, which possess coarser grains along with ultrafine grains, are responsible for increasing ductility (24.7%) and fracture toughness (115.8?kJ/m²). The microstructural characterization of the deformed material was performed through optical microscopy, X-ray diffraction, SEM fractography, and TEM and it was correlated with the tensile and fracture characteristics of the alloy.     

退火热处理对TA15钛合金组织性能的影响

研究了不同的退火热处理制度对TA15钛合金显微组织、室温拉伸性能、高温拉伸性能、室温冲击韧性及硬度的影响。结果表明：在相变点以上温度退火,合金具有较高的室温、高温强度,但室温塑性、高温塑性、室温冲击韧性较低;在相变点以下温度退火,合金的室温、高温断裂强度在860℃退火时出现峰值,而室温塑性、高温断面收缩率和室温冲击韧性则随着退火温度的升高而提高;同单重退火相比,双重退火、三重退火对提高合金性能的作用不大。     

Using Post‐Deformation Annealing to Optimize the Properties of a ZK60 Magnesium Alloy Processed by High‐Pressure Torsion

A ZK60 magnesium alloy with an initial grain size of ≈10 µm is processed by high‐pressure torsion (HPT) through 5 revolutions under a constant compressive pressure of 2.0 GPa with a rotation speed of 1 rpm. An average grain size of ≈700 nm is achieved after HPT with a high fraction of high‐angle grain boundaries. Tensile experiments at room temperature show poor ductility. However, a combination of reasonable ductility and good strength is achieved with post‐HPT annealing by subjecting samples to high temperatures in the range of 473–548 K for 10 or 20 min. The grain size and texture changes are also examined by electron back scattered diffraction (EBSD) and the results compared to long‐term annealing for 2500 min at 450 K. The results of this study suggest that a post‐HPT annealing for a short period of time may be effective in achieving a reasonable combination of strength and ductility.

     

Fatigue behaviour of dissimilar Al 5052 and Mg AZ31 resistance spot welds with Sn‐coated steel interlayer

The fatigue property of dissimilar spot welds between an aluminium alloy (AA5052) and a magnesium alloy (AZ31) was studied in this research. The AA5052 and AZ31 coupons were resistance spot welded together by using an interlayer of Sn‐coated steel between the two coupons. The fatigue test results revealed that the Mg/Al joints had the same level of fatigue strength as Mg/Mg resistance spot welds. It was found that within the life range of N_f < 10⁵ cycles, Mg/Al welds degraded faster than Mg/Mg joints. This was attributed to the larger bending moment on the plane of fatigue failure in the Mg/Al welds. Three failure modes were observed under different cyclic loading regimes: Al/steel interfacial failure, Mg coupon failure and Al coupon failure. Fatigue fracture surface of Mg/Al welds consisted of two distinct regions: crack propagation region with brittle morphology and final rupture with ductile morphology.     

Tensile behaviour of Ni3Al+B intermetallic compound: influence of cold deformation and annealing

Nickel aluminide, intermetallic compound Ni₃Al, is a promising structural material on account of its high strength at elevated temperatures. The influence of cold deformation on the tensile behaviour of an Ni₃Al alloy containing zirconium and boron is presented. The undeformed material, in the as-cast condition, was subjected to varying levels of cold deformation ranging from 11.4%–61.4%, and tensile tests performed. The tensile properties and fracture behaviour of the cold-deformed material are compared with undeformed material to highlight the influence of cold deformation on strength, ductility and fracture behaviour. Tensile tests were performed on cold-deformed plus annealed samples and properties compared with the cold-deformed counterpart in order to elucidate the influence of annealing on tensile behaviour. The intrinsic effects of cold deformation and annealing on microstructure, tensile properties and fracture behaviour are highlighted.