Despite the great potential of Mg and its alloys as material for biodegradable implants, their low resistance to the simultaneous action of corrosion and mechanical stresses in the human body have ...hampered their use. Stress Corrosion Cracking has been reported as one of the most critical failure modes to overcome to allow such materials to be clinically applied. Thus, in this paper we investigate the effect of Equal Channel Angular Pressing (ECAP) on the Stress Corrosion Cracking (SCC) susceptibility of the AZ31 Mg alloy. To do so, AZ31 alloy has been subjected to 1, 2 and 4 passes of ECAP, and the samples so obtained have then been tested by means Slow Strain Rate Tests (SSRTs) in Simulated Body Fluid (SBF) at 37 °C. Samples subjected to one pass of ECAP are shown to be less susceptible to SCC compared to the material in the as-received condition, while further ECAP processing (2 and 4 passes) are found to worsen the SCC susceptibility. To understand the different SCC susceptibilities shown by the differently ECAPed samples, microstructural analyses, potentiodynamic polarization curves, hydrogen evolution experiments and Scanning Electron Microscopy (SEM) analyses of the fracture surfaces were carried out. The improved corrosion resistance of the samples subjected to 1 pass of ECAP compared to the samples in the as received condition (due to a finer grain size) and to the samples subjected to 2 and 4 passes (due to a more favourable texture evolution) represents the reason of their reduced SCC susceptibility.
► A warm pre-stretching process was carried out on AZ31 magnesium alloy. ► This process increased the grain size and weakened the basal texture. ► The pre-stretched sample showed much larger fracture ...elongations in both directions. ► The IE of the pre-stretched sample was increased by ∼54%, which meant better formability.
A pre-stretching process was carried out at 250°C to improve the microstructure of an AZ31 alloy to investigate its effects on microstructure and properties. This process produced two effects on the microstructure: slight increasing of the grain size and texture weakening. The microtexture and macrotexture data showed that the c-axis of some grains tended to rotate towards the transverse direction after warm pre-stretching. Compared with the as-received sample, the pre-stretched sample exhibited larger fracture elongations both in the rolling direction and transverse direction. Erichsen tests were conducted at room temperature to evaluate influence of warm pre-stretching on the press formability of AZ31 alloy sheets. Here, the Erichsen value (IE) of the pre-stretched sample was increased by ∼54%.
AZ31 magnesium alloy sheets were processed using unidirectional rolling (UR) and three-directional rolling (TDR) followed by annealing. Compared with UR, TDR produced finer grain microstructure, ...weaker basal texture and thus led to a larger Schmid factor at different rolling reductions due to the alternating changing direction of tensile stress and compressive stress during rolling. The mechanical properties, e.g. strength, strength anisotropy and failure elongation of the UR and TDR samples were investigated at room temperature. Enhanced mechanical properties of AZ31 alloy sheets processed by TDR were obtained by grain refinement and weakening basal texture.
AZ31 magnesium alloy sheets were prepared by low-speed extrusion at different temperatures, i.e., 350 °C, 400 °C, and 450 °C. The microstructure evolution and mechanical properties of extruded AZ31 ...magnesium alloy sheets were studied. Results indicate that the low-speed extrusion obviously improved the microstructure of magnesium alloys. As the extrusion temperature decreased, the grain size for the produced AZ31 magnesium alloy sheets decreased, and the (0001) basal texture intensity of the extruded sheets increased. The yield strength and tensile strength of the extruded sheets greatly increased as the extrusion temperature decreased. The AZ31 magnesium alloy sheet prepared by low-speed extrusion at 350 °C exhibited the finest grain size and the best mechanical properties. The average grain size, yield strength, tensile strength, and elongation of the extruded sheet prepared by low-speed extrusion at 350 °C were ~2.7 μm, ~226 MPa, ~353 MPa, and ~16.7%, respectively. These properties indicate the excellent mechanical properties of the extruded sheets prepared by low-speed extrusion. The grain refinement effect and mechanical properties of the extruded sheets produced in this work were obviously superior to those of magnesium alloys prepared using traditional extrusion or rolling methods reported in other related studies.
The stamping formability of Mg–3Al–1Zn (AZ31) alloy was greatly enhanced through weakening (0001) basal texture by repeated unidirectional bending (RUB). After RUB and subsequent annealing, the max ...(0001) texture intensity of AZ31 Mg alloy was weakened from 10.7 to 6.3 and thus the Schmid factor for basal slip system increased from 0.25 to 0.29. The RUB prepared AZ31 Mg alloy in annealed condition possessed better stamping formability than the original sheet at 373 K, e.g., larger Erichsen value (7.5 mm vs. 5.5 mm), higher and wider forming limit diagram (FLD), larger limiting drawing ratio (LDR) (1.7 vs. 1.4). The weakened (0001) basal texture resulted in a lower Lankford value (r-value) and a higher strain hardening exponent (n-value), thus enhancing the stamping formability of AZ31 Mg alloy. For the deep-drawing cup of the RUB fabricated AZ31 Mg alloy, a weakened (0001) texture and a high Schmid factor of basal slip system were still remained in the internal area, the central area and the external area of the corner in comparison to the deep-drawing cup of the original AZ31 Mg alloy.
The development of customised aluminium alloys for welding and additive manufacturing (AM) is proposed to solve several quality issues and to enhance the mechanical integrity of components. The ...introduction of ceramic grain refining agents shows great potential as alloy addition as to limit cracking susceptibility and increase the strength. Thus, a versatile solid-state manufacturing route for nanoparticle reinforced aluminium wires has been developed based on the metal screw extrusion principle. In fact, the Al-Si alloy AA4043 mixed with 1 wt.% TiC nanoparticles has been manufactured as a wire. The accumulated strain on the material during metal screw extrusion has been estimated, classifying the process as a severe plastic deformation (SPD) method. A chemical reaction between silicon and TiC particles after metal screw extrusion was found, possibly limiting the grain refining effect. Electric arc bead-on-plate deposition was performed with metal screw extruded and commercial material. The addition of TiC induced a grain morphology transition from columnar to equiaxed after electric arc deposition, and increased the hardness. A high amount of porosity was found in the AA4043-TiC material, probably arising from hydrogen contamination on TiC surfaces prior to metal screw extrusion. The results are encouraging as a new direction for aluminium alloy development for additive manufacturing.
In this study, an in situ SEM/EBSD study on slip-induced extension twinning (S→T) behaviors of a Mg–Y alloy was conducted. It shows that the S→T process cannot be well explained using the classical ...geometrical compatibility parameter (m') determined by macroscopic stress. A new experimental method is proposed to unequivocally determine the slip directions of the source slip systems by combining the lattice rotation analysis and the slip trace analysis. By using the experimentally determined active slip systems, the validity of m' to reveal the S→T mechanism is improved. By a detailed study on lattice rotations of the grains containing source slip for twinning, it is found that the S→T process is dominated by micro deformation instead of macro deformation. This study emphasizes the importance of considering the effect of microscopic deformation when attempting to understand the S→T process in deformed magnesium alloys.
•Slip-induced extension twinning (S.→T) behaviors in a Mg–Y alloy were investigated by in situ SEM/EBSD.•Lattice rotation analysis showed that the S.→T process is dominated by micro deformation instead of macro deformation.•A new experimental method was proposed to unambiguously reveal the real source slip system in the S.→T process.•The validity of the classical geometrical compatibility parameter (m') to explain the S.→T mechanism was improved.
•Three rolling routes were carried out on AZ31 alloy.•Route B and Route C rolling produced finer recrystallized grains and weaker basal texture.•Route B and Route C rolling produced larger Schmid ...factor than Route A rolling.•Route B and Route C rolled samples exhibited higher tensile strengths and fracture elongations.•Route B and Route C rolling effectively enhanced the formability of AZ31 alloy at room temperature.
Influence of three rolling routes on the microstructure evolution and properties of AZ31 magnesium alloy sheets was investigated. Route A is unidirectional rolling where the rolling direction is always the same, Route B is cross rolling where each rolling direction changes at 90° and Route C where the rolling direction is changed by 45° around the normal direction after each cross rolling. The results indicate that compared with the Route A rolled sample, the Route B and Route C rolled samples produce finer recrystallized grains and weaker basal texture due to the alternating changing direction of tensile stress and compressive stress during rolling. The average Schmid factors of the Route B and Route C rolled samples are also greatly increased due to the significantly weakened basal texture. Furthermore, the Route B and Route C rolled samples exhibit higher tensile strengths, larger fracture elongations and higher Erichsen values than Route A rolled sample, which can be attributed to the finer grains and weaker basal texture.
A high-throughput gradient thermal compression process was adopted to investigate the effects of thermal deformation parameters on the deformation behavior and microstructure evolution of a rolled ...AZ31 Mg alloy. The results showed that with increasing deformation degree, the flow stress-strain curves of the double-cone samples compressed along the normal direction (ND), transverse direction (TD), and rolling direction (RD) of rolled Mg alloy rapidly reached their peak value, then decreased gradually, and finally maintained a trend of horizontal change. Under the same strain condition, the dynamic recrystallization (DRX) degree of the double-cone sample increased gradually with increased deformation temperature. Twins were more likely to occur when compression occurred in the TD and RD, rather than along ND. With increasing temperature or strain, the number of twins that formed during compression gradually decreased. At deformation temperatures of 250 °C and 300 °C, continuous dynamic recrystallization was the main DRX mechanism in the double-cone samples compressed along the ND, TD, and RD. Furthermore, the twin-assisted DRX mechanism also occurred in the double-cone samples compressed at 250 °C along the TD and RD. During compression at 350 °C and 400 °C along the ND, TD, and RD, discontinuous dynamic recrystallization occurred in the double-cone samples, indicating that the DRX mechanism changed with increasing compression temperature.
Deep drawing experiments carried out at 473K revealed that the AZ31 magnesium alloy sheets could be successfully drawn at a limiting drawing ratio (LDR) of 2.3 with a drawn depth of 54mm. ...Microstructural and textural evolution in different region of the drawn cup were investigated. In the bottom region which was subject to no deformation, the microstructure and basal texture showed almost no changes. Some fine recrystallization grains appeared in the shoulder region with small thickness strain and the basal texture showed almost no changes. In the wall region with 40% thickness strain, more recrystallization grains were observed, the c-axis of the grains tended to rotate toward the transverse direction (TD) of the rolled sheets and the basal texture evolved into an elongated shape around the normal direction (ND) with the elongated direction perpendicular to the deep drawing direction. A great deal of fine recrystallization grains formed in the edge region with 85% thickness strain and the basal texture dramatically changed to the c-axis//TD texture with basal planes perpendicular to the sheet plane. The formation of this c-axis//TD texture is caused by the activation of non-basal slip systems due to the high deformation temperature. Analyses on basal slip and non-basal slip systems by Schmid factors were carried out to discuss the deformation behavior during deep drawing.
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