Room Temperature Formability Research Articles

Great room temperature stretch formability of fine-grained Mg-Mn alloy

The effect of grain size and forming speed on room temperature formability was examined using Mg-0.3at%Mn binary alloy with different average grain sizes (2.5 and 18.5µm). Erichsen tests revealed that the limited dome height (LDH) was clearly influenced by these factors. LDHs increased with finer grain sizes and/or lower forming speeds. The highest LDH was obtained to be 8.2, which is superior to that in the conventional aluminum (A5083) alloy (LDH=4.3), in the present Erichsen testing conditions. The results obtained from the tensile tests under strain rate ranges similar to those of the Erichsen tests showed high strain rate sensitivity (m-value, where m=0.06–0.13 for the meso-grained alloy and 0.11–0.22 for the fine-grained alloy, respectively), irrespective of the extrusion direction vs. the tensile direction. Deformed microstructural observations after tensile and Erichsen tests revealed the existence of deformation twinning; however, the area/volume fraction of its microstructural feature was too small to affect the deformation mechanism. Instead of the deformation twinning-related fracture, cavitation due to grain boundary sliding was the origin of fracture during the present Erichsen tests. The further activation of grain boundary sliding was an effective method to improve the room temperature formability of magnesium alloys.

Development of Room Temperature Formability of Rolled Magnesium Alloy Sheets by Texture Control

Development of Room Temperature Formability of Rolled Magnesium Alloy Sheets by Texture Control

The influence of Ca and Gd microalloying on microstructure and mechanical property of hot-rolled Mg-3Al alloy

Abstract After hot rolling magnesium alloy sheets exhibit an intensive basal texture, leading to its low formability at room temperature. Microalloying is an effective, practicable and economical measure to improve the comprehensive performance of magnesium alloy, especially for taking Ca and Gd as main components recently which greatly increases the room temperature formability of magnesium alloy by attenuating or tilting the basal texture. In this study some Mg-3Al alloys with Ca single and Ca-Gd combined microalloying were hot rolled at 673K and annealed at 623K for 1h. The effect of addition of Ca and Gd on microstructure, texture and tensile properties of Mg-3Al series alloy were investigated. The results showed that the single addition of Ca element can attenuate basal texture and improve room temperature formability of Mg-3Al alloy, but limitedly refine grain size. The combined addition of microalloying Ca and Gd element can significantly attenuate basal texture and improve refinement of grain size and room temperature formability of Mg-3Al alloy, also reduce the anisotropy of mechanical property. The main reason for attenuating basal texture is that the recrystallization behavior is delayed due to the secondary phase. The attenuating of basal texture and the activation of non-basal slip systems are the mechanism of the reduced anisotropy.

A Critical Review of Mg–Zn–Y Series Alloys Containing I, W, and LPSO Phases

Magnesium and its alloys are playing an increasingly important role in the transportation industry due to the pressing demand of lightweight structures to improve fuel efficiency and reduce CO2 emissions. But the shortcomings of poor room temperature (RT) formability and high temperature strength, tension–compression asymmetry, and anisotropy are among the major issues which are currently limiting their widespread applications. Recently, research and development activities of Mg–Zn–Y series alloys have significantly increased because of their superior mechanical properties arising from the formation of different ternary phases known as I (Mg3YZn6), W (Mg3Y2Zn3), and LPSO (Mg12YZn). In this review article, the crystal structure of these phases and their orientation relationships with hexagonal magnesium matrix are discussed. Recent advances about I, W, and LPSO phase containing Mg alloys are presented, along with the effects of these phases on the microstructural evolution and mechanical properties including tensile, compressive, fatigue, and creep resistance. Important aspects involving thermal stability, phase transformation, and influence of heat treatment are also described. Based on the current status, some existing issues are pointed out and further studies are suggested so as to warrant safe and reliable lightweight structural applications of Mg–Zn–Y alloys in the automotive industry.

Deformation behaviors of twin roll cast Mg-Zn-X-Ca alloys for enhanced room-temperature formability

Formability and viscoplastic self-consistent simulations of Mg-4Zn-X-Ca alloys were carried out in an effort to understand the relationship between deformation behaviors and room-temperature formability. The microstructural, textural and mechanical properties of Mg-4Zn-X-Ca alloys were also investigated. All of the alloys showed a sound twin roll cast microstructure without the occurrence of inverse segregation. Annealed Z4 and ZSX400 alloys exhibited strong basal textures; however, the other Mg alloys showed weaker basal textures with splitting in the transverse direction resulting from their different types of static recrystallization. Among the Mg-4Zn-X-Ca alloys, the ZAX400 alloy exhibited a high yield strength value of 189.3MPa and excellent formability of 7.5mm with enhanced yield isotropy, comparable to those of Al alloys. The higher formability values of the Mg-4Zn-X-Ca alloys were closely related to the modified deformation behaviors resulting from the texture evolution. The ZX40, ZAX400, ZWX400 and ZCX400 alloys, which were more formable, had higher relative activity of the basal <a> slip upon compression deformation, thus improving the yield isotropy. However, the Z4 and ZSX400 alloys in this study, had relatively low activity of the basal <a> slip in compression modes, as caused by their different CRSS ratios (tension twin/basal <a> slip).

Enhancement of room temperature stretch formability via grain boundary sliding in magnesium alloy

The enhancement method of room temperature formability was investigated by controlling the rate-controlling mechanism. Wrought processed pure magnesium and its alloys (Mg-Al-Zn and Mg-Mn alloys), which have a basal texture, were used in this study. Pure magnesium had two kinds of average grain sizes (~7µm and ~30µm), and the other alloys were 20–30µm in average grain size. The forming load vs. displacement curves in Erichsen tests were not influenced by the forming rate in the Mg-Al-Zn alloy; however, the fine-grained pure magnesium and Mg-Mn alloy showed a high forming rate dependence. The limited dome heights were 4.7, 2.0 and 5.2 for the fine-grained pure magnesium, Mg-Al-Zn and Mg-Mn alloys, respectively. Deformed microstructural observations revealed that, in the meso-grained pure magnesium and the Mg-Al-Zn alloy, deformation twins formed and were closely related to crack propagation. On the other hand, the formation of such deformed structures was difficult to identify in the fine-grained pure magnesium and meso-grained Mg-Mn alloy. The good stretch formability and high rate dependence of the fine-grained pure magnesium and Mg-Mn alloy resulted from the major contribution of grain boundary sliding to deformation during Erichsen testing. The addition of an alloying element, which plays a role in the enhancement for grain boundary sliding, is quite effective to improve the room temperature stretch formability.

Thermo-Kinetic Modelling and Analysis of the Simultaneous Hot Stamping and Quenching of EN AW-6016-T4 Sheet

The aluminium alloy AW-6016-T4 sheet is the most widely used alloy for simple-shapeouter body parts for passenger vehicles at room temperature. However, for complex parts, such asthe B-pillar, the room temperature formability of AW-6016-T4 sheet is not sufficient. Simultaneoushot stamping and quenching is a viable alternative, but there is still limited information about theinfluence of process parameters on both the formability during the process and the part strength atthe end of the process. A combination of thermo-kinetic simulation and experiments were used toinvestigate the influence of process parameters in the simultaneous hot stamping and quenchingprocess.Increasing the heating rate from 1 to 100 K s-1 during heating to the solution heat treatment (SHT)temperature was found to have no significant influence on the UTS. However, a SHT time of 4 minis required to achieve highest strength by the end of the process chain. Increasing the amount ofdeformation and cooling rate after SHT have a positive influence on the finished part. PredictedDSC curves and Yield strength values from MatCalc were in good agreement with the experimentalresults.

Single Point Incremental Forming of an Aged AL-Cu-Mg Alloy: Influence of Pre-heat Treatment and Warm Forming

This research is aimed at enhancing the poor room temperature formability of heat-treatable aluminum alloy AA2024-T3, without deterioration of its post-forming properties. For this purpose, the influences of different heat-treatment conditions as well as warm forming on the single point incremental forming formability and post-forming properties of this material were investigated. Thermal pre-treatments were consisting of annealing (O-temper), solution treating and quenching (W-temper), and solution heat treating, quenching, and then cold working (T-temper). The formability results as well as forming forces of pre-heat-treated sheets were compared to those of the warm forming process results carried out using a laser-assisted single point incremental forming (LASPIF) setup. The post-forming properties of SPIF-formed parts were analyzed by hardness testing. The maximum forming angles of the blank formed under O-temper and W-temper conditions showed, respectively, 41 and 32% increases compared to the one under T-temper condition. LASPIF forming of this material at a temperature of about 360 °C resulted in 41% improvement in the maximum forming angle with respect to parts formed at room temperature from the T-temper sheet. The hardness of the material reduced significantly after annealing, while SPIF parts formed from W-temper blanks and under LASPIF condition regained their hardness after natural aging. The fracture surface characteristics of the failed parts showed that voids nucleate at the interface between intermetallic particles and matrix, and a dimple rupture fracture mode was identified under all heat-treatment conditions. Under O-temper condition, due to precipitation of particles along the grain boundary, an intergranular dimple rupture was observed. Finally, Energy dispersive x-ray (EDX) and electron backscattered diffraction (EBSD) were used to investigate the possible effects of the heat treatment and the deformation on the changes in the composition of intermetallic and second-phase particles, grain size, and texture.

Investigation of texture, microstructure, and mechanical properties of a magnesium–lanthanum alloy after thermo-mechanical processing

Abstract The texture, microstructure, and mechanical properties of Mg-1.33La (wt.%) alloy after hot rolling and cold plane strain compression were investigated by using X-ray diffraction, optical microscopy, and micro-hardness measurements. This thermo-mechanical processing resulted in a relative weakening of the texture that was mainly a basal type. The microstructures after hot rolling and cold plane strain compression revealed the presence of a second phase (Mg17La2), mostly at grain boundaries. Twins were profuse, and their morphologies were quite different after hot rolling and cold plane strain compression. The Mg-1.33La (wt.%) alloy exhibited good room temperature formability and an increase in strength. The alloy's hardness increased with increasing deformation strain. Such properties were explained by the effect of both the Mg17La2 phase precipitation and the sample's texture.

Finite Element Analysis of hot Single Point Incremental forming of hip prostheses

The titanium alloy Ti-6Al-4V is one of the most frequently used materials for biomedical applications due to its biocompatibility and excellent mechanical properties. However, wide usage of Ti-6Al-4V sheet is limited by its poor room-temperature formability. Therefore, hot Single Point Incremental Forming (SPIF) has been used to improve its formability. This paper aims at proving the feasibility of the hot incremental forming of an acetabular component of hip prosthesis by Finite Element simulations. The effect of process parameters, namely the forming temperature and the punch diameter on the geometric accuracy and the failure of the final product are investigated.

Warm forming limits of rare earth-magnesium alloy ZEK100 sheet

Forming limit curves were developed for a rare earth-magnesium alloy, ZEK100-F, at temperatures between 25 and 350 °C in both the rolling (RD) and transverse directions (TD) of the sheet. ZEK100-F contains additions of zirconium (Zr) as a grain refining alloying element and a rare earth addition, neodymium (Nd), that promotes a weakened basal texture allowing enhanced slip activity at lower temperatures. Warm formability measurements were also performed on non-rare earth containing AZ31B-O to examine the relative performance of these two alloys. The ZEK100 material exhibited significantly better room temperature formability over AZ31B-O with a limiting dome height of 29 mm for ZEK100 compared to only 12 mm for the AZ31B-O. At elevated temperatures (250 °C) the difference in formability between the two alloys becomes less pronounced with a LDH of 40 and 36 mm for ZEK100 and AZ31B-O, respectively. What is particularly striking is the pronounced benefit of the rare earth alloyed material at intermediate temperatures, with an LDH of 37 mm at 150 °C which equals the LDH of AZ31B at 250 °C. Similar trends were determined in the measured forming limit curves reported here for the two alloys. The relative performance of the two alloys is largely attributed their initial textures. ZEK100-F also exhibits strongly anisotropic formability (RD versus TD) which can again be attributed to its’ initial texture.

A three dimensional (3D) thermo-elasto-viscoplastic constitutive model for FCC polycrystals

Elevated temperature has significant effect on the mechanical response of metals and alloys. Industrial processes often use high temperature forming to fabricate components of complex shape from alloys such as aluminum or magnesium that have low room temperature formability. Accurate forming models to integrate warm forming in computer aided engineering (CAE) in production environment has been hampered by a lack of constitutive relations at elevated temperatures, forcing one to rely on experimental data for such integration. In this paper, a new thermo elasto-viscoplastic (TEV) constitutive relation is developed to model the behavior of face-centred cubic (FCC) polycrystals, especially aluminum alloys, at elevated temperatures. The model takes into account the temperature dependence of the single crystal elastic coefficients, single slip hardening parameters, thermal softening, rate sensitivity, and the total deformation. The TEV framework has been implemented into the commercial finite element code LS-DYNA to study the effects of temperature on metal forming. Uniaxial tension simulations at six different temperatures ranging from 25 °C to 260 °C have been performed and calibrated with published experimental results. Equations for the variation of single-slip hardening parameters with temperature have been developed for the AA5754 aluminum alloy. Shear test simulations at different temperatures have been used to validate the model. The proposed framework for the single slip parameters for uniaxial tension accurately predicts the shear stress-shear strain data without the need for any further fitting parameter. Temperature dependence of texture evolution, single slip hardening and hardening rates, thermal softening, and slip activity in AA5754 sheet alloy during temperatures corresponding to warm forming temperatures are investigated.

Effect of hot working on the damping capacity and mechanical properties of AZ31 magnesium alloy

Magnesium alloys have received much attention for their lightweight and other excellent properties, such as low density, high specific strength, and good castability, for use in several industrial and commercial applications. However, both magnesium and its alloys show limited room-temperature formability owing to the limited number of slip systems associated with their hexagonal close-packed crystal structure. It is well known that crystallographic texture plays an important role in both plastic deformation and macroscopic anisotropy of magnesium alloys. Many authors have concentrated on improving the room- temperature formability of Mg alloys. However, despite having a lot of excellent properties in magnesium alloy, the study for various properties of magnesium alloy have not been clarified enough yet.Mg alloys are known to have a good damping capacity compared to other known metals and their alloys. Also, the damping properties of metals are generally recognized to be dependent on microstructural factors such as grain size and texture. However, there are very few studies on the relationship between the damping capacity and texture of Magnesium alloys. Therefore, in this study, specimens of the AZ31 magnesium alloy, were processed by hot working, and their texture and damping property investigated. A 60 mm × 60 mm × 40 mm rectangular plate was cut out by machining an ingot of AZ31 magnesium alloy (Mg-3Al-1Zn in mass%), and rolling was carried out at 673 K to a rolling reduction of 30%. Then, heat treatment was carried out at temperatures in the range of 573-723 K for durations in the range of 30-180 min. The samples were immediately quenched in oil after heat treatment to prevent any change in the microstructure. Texture was evaluated on the compression planes by the Schulz reflection method using nickel-filtered Cu Kα radiation. Electron backscatter diffraction measurements were conducted to observe the spatial distribution of various orientations. Specimens for damping capacity measurements were machined from the rolled specimen, to have a length of 120 mm, width of 20 mm, and thickness of 1 mm. The damping capacity was measured with a flexural internal friction measurement machine at room temperature. It was found that the damping capacity increases with both increasing heat-treatment temperature and time, due to grain growth and the increased pole densities of textures.

Modified texture and room temperature formability of magnesium alloy sheet by Li addition

The effect of Li addition on the mechanical responses of magnesium alloy sheets was examined in correlation with the concurrent microstructure and texture evolution. The basal texture was drastically weakened and the basal pole rotated to the transverse direction (TD) owing to the Li addition. The Mg alloy sheet containing lithium element exhibited larger uniform elongation and its Erichsen value (IE) increased by ~ 59 %. Enhanced the ambient formability of the extruded Mg alloy sheet fabricated by Li addition was accomplished by the tilted weak basal texture. The microstructure evolution and properties were characterized and compared.

Twinning and texture evolution in binary Mg-Ca and Mg-Zn alloys

Texture evolution and formability in binary Mg-Ca and Mg-Zn alloys have been investigated in the present study. Static recrystallization during annealing treatment of rolled sheets leads to increase of basal pole intensity in Mg-3Zn alloy, but decrease in Mg-xCa alloys (x=0.05, 0.1 and 0.5). With increasing Ca content in Mg-xCa alloys, the basal texture becomes weaker, indicating that Ca is one of the effective elements in weakening the basal texture in Mg alloys. The effect of Ca on weakening the basal texture mainly comes from the presence of Ca atoms in the α-Mg solid solution matrix rather than from the Mg2Ca particles formed during solidification. More frequent occurrence of compression (or double) twins results in weakening of the basal texture possibly due to lower stacking fault energy in Mg-Ca alloy than in Mg-Zn alloy. The room temperature formability of Mg-Ca alloy is highly superior to that of the Mg-Zn alloy.

Effect of Li addition on microstructure and mechanical properties of Al – Mg – Si alloy

Abstract The ever increasing utilization of Al – Li alloys for light weight structural applications is limited chiefly due to their lower room temperature formability compared to their Li-free counterparts. In the present work, the effect of 1, 2 and 3 wt.% Li addition to Al – Mg – Si alloy (containing 0.5 wt.% Mg and 0.2 wt.% Si) was studied. Experimental work showed that microstructural features of the second phase particles and mechanical properties changed substantially with Li addition. It was observed that 1 wt.% Li addition resulted in significantly large elongation of over 38 % resembling a super-plastic behavior with decent strength and hardness due to the formation of second phase precipitates uniformly dispersed in α (Al) matrix. Scanning electron microscopy and X-ray diffraction analysis revealed that the addition of Li promotes the formation of second phase precipitates, which strongly affect the mechanical properties of Al – Mg – Si alloy. Quite surprisingly, the alloys containing 2 and 3 wt.% Li showed a much reduced ductility and a much higher hardness after aging.

Three Point Bend Performance of Solutionized, Die Quenched and Heat Treated AA7075 Beam Members

To overcome the low room temperature formability of AA7075-T6 aluminum sheet, without sacrificing the high strength properties of this alloy, a hat section beam member was formed and quenched within a cold die immediately after a 20 minute solutionizing treatment. Natural aging for 24 hours followed the forming process which was then followed by various heat treatments that included a typical precipitation hardening (PH) and industrial paint bake (PB) temperature-time treatment. Tensile specimens were extracted from the beams to evaluate their mechanical properties. When compared to the as-received AA7075-T6 mechanical properties, the beams heat treated with the PH, PHPB and PB treatment resulted in a 5%, 13% and 20% reduction in ultimate tensile strength respectively. A similar trend was shown for the yield strength measurements. There was little effect of the heat treatments on the total elongation, with the PH condition showing a slight improvement. A backing plate was riveted to the beams and a quasi-static 3 point bend test was conducted to evaluate the crush performance. The peak load for the PH, PHPB and PB beams was 9.2, 8.5 and 7.3 kN respectively, but the calculated energy-displacement (or energy absorption) curves were similar for the PH and PHPB parts due to a more ductile fracture behavior for the PHPB material condition.

A mechanism-dependent material model for the effects of grain growth and anisotropy on plastic deformation of magnesium alloy AZ31 sheet at 450 °C

Utilization of wrought magnesium sheet alloys for structural components in transportation industries has been severely limited by poor room-temperature formability, a result of the slip behaviors inherent to Mg’s hexagonal close-packed crystal structure. Today, the only production technology to clearly overcome this limitation uses hot forming to activate additional (non-basal) slip systems in Mg alloy sheet. The absence of an accurate material constitutive model that captures the complex mechanical response of Mg sheet alloys at elevated temperatures has been a persistent barrier to accurate forming simulations. This study addresses that issue using experimental measurements and mechanism-based modeling. The mechanisms of plastic deformation in a Mg AZ31 wrought alloy sheet at 450°C across strain rates from 10−4 to 10−1s−1 are identified as grain-boundary-sliding (GBS) creep and five-power dislocation-climb (DC) creep. GBS creep is subject to hardening from grain growth, and DC creep produces texture-dependent plastic anisotropy. Based on these mechanisms, a new material constitutive model for Mg AZ31 at 450°C is constructed to predict plastic response under general multiaxial loading. A unique aspect of this new model is that it accounts for hardening and plastic anisotropy by linking these effects to the two mechanisms controlling deformation. The model is validated against independent experimental data and provides accurate predictions for hot forming of a simple test shape. The new material model is the first for Mg AZ31 sheet that accurately predicts deformation at an elevated temperature under both uniaxial and biaxial stress states.

Texture evolution during annealing of AZ31 Mg alloy rolled sheet and its effect on ductility

Magnesium sheet alloys have huge potential in automotive closure applications due to their light weight. However, their limited room temperature formability restricts their widespread applications. Microstructure (both geometric and crystallographic) plays a key role in dictating the formability of an alloy. In this research, a systematic study of the microstructure evolution of a hot-rolled AZ31 sheet during thermal annealing was carried out, and the effect of microstructure on room-temperature deformation was characterized. The initial hot-rolled sheet had a dominant basal texture with equiaxed grains and shear bands. The annealing treatment imparted to the sheet alloy triggered an anomalous, inhomogeneous grain growth in grains with a large deviation from the basal orientation. At 350°C annealing temperature, a bimodal grain size distribution of grains with basal and non-basal orientations was observed, and this combination was shown to significantly enhance ductility resulting from a complex interplay between slip and twinning deformation mechanisms. This key finding is expected to contribute to the development of engineered microstructures for enhanced room temperature formability in this alloy.

Texture Formation and Room-Temperature Formability of Rolled Mg&amp;ndash;Zn&amp;ndash;Ce Alloys

Texture Formation and Room-Temperature Formability of Rolled Mg&amp;ndash;Zn&amp;ndash;Ce Alloys