Magnesium-based alloys are being used today in various lightweight applications. The mechanical properties of magnesium-based alloys can be enhanced for such applications through a combination of annealing temperature and holding time of the magnesium-based alloy. The magnesium-based alloy under investigation in this study is Mg-5%Zn. The results of this investigation show that optimizing annealing time and temperature can achieve homogenization and enhance the mechanical properties and formability of Mg-5%Zn as seen in hardness test results for the homogenized samples.
Hot isostatic pressing (HIP) treatment after solution treatment has been investigated on its effects on the mechanical and corrosion properties of Mg-Gd-Y-Zn alloys with high long-period stacking order (LPSO) 14H phase fractions. Plate and cylinder samples of three different compositions were cut from permanent mold castings. The alloy samples were solution treated for 25 h at 500 °C and processed with the following HIP conditions: 485–490 °C, 100–200 MPa, for 2 h. The mechanical properties generally increased with HIP. Under accelerated corrosion conditions (submersion in 3% KCl at a temperature of 90 °C), the corrosion rate was observed to increase after HIP. HIP was found not to change the density of the samples, indicating micro-porosity was not an issue. The change in corrosion rate and mechanical properties were a result of microstructural changes due to the HIP thermal cycle. CALPHAD (CALculation of PHAse Diagrams) modeling of the three compositions as well as scanning electron microscopy (SEM) microstructural observations of the alloys are provided.
The intrinsic low density of magnesium drives research towards high-performance magnesium alloys. Hierarchically structured ultrafine grained magnesium alloys possess exceptional strength-ductility combination and eliminate many of the traditional drawbacks like low strength, high yield strength asymmetry, poor formability, and limited superplasticity. In this overview presentation, friction stir processed microstructures are used as examples to discuss the microstructural paradigms that can exhibit excellent balance of mechanical properties. These show the possibilities of exceeding 500 MPa strength with good work hardening and >10% ductility. Use of micron-sized boron carbide (B4C) and nano-sized yttria (Y2O3) powder can simultaneously enhance modulus-strength-ductility combination. High-strength ultrafine grained magnesium alloys also show high strain rate superplasticity which can provide pathways for overcoming poor formability. An example of friction stir additive manufacturing will be used to discuss possibilities of implementing such microstructures at component level with emerging solid-state additive manufacturing techniques.
We investigated the effects of Zn additions on the mechanical properties and microstructure of Mg–1.2Al–0.5Ca–0.4Mn and Mg–1.2Al–0.5Ca–0.4Mn–1.6Zn (wt%) alloy sheets fabricated by twin-roll casting and conventional hot rolling. The room temperature stretch formability of the solution-treated alloy sheet is improved by the addition of Zn. The Mg–1.2Al–0.5Ca–0.4Mn–1.6Zn alloy shows an excellent stretch formability with the larger Index Erichsen value of 8.2 mm due to a weak transverse direction split texture. The development of the weak texture is attributed to the uniform grain growth by the solute segregation to the recrystallized grain boundaries. Subsequent bake-hardening treatment, 2% pre-strain at 170 °C for 20 min leads to substantial increase in strength without the loss of ductility. The bake-hardened Mg–1.2Al–0.5Ca–0.4Mn–1.6Zn alloy exhibits a high tensile yield strength of 235 MPa with an elongation to failure of 27.1%.
Extended Abstract Magnesium (Mg) alloys have attracted considerable attention for a promising application in the automotive and electronics owing to their high specific strength and high electromagnetic shielding. However, the application of wrought Mg alloys has been limited by poor room temperature ductility. It was ascribed to the large difference in critical resolved shear stresses (CRSS) between basal and prismatic slip in hexagonal close-packed (hcp) crystal structure in Mg alloy . This results in a lack of the active slip systems and can hardly offer an arbitrary shape change at the grain level. Conventionally extruded Mg alloy sheets possess poor mechanical properties due to the strong basal texture where c-axes of the grains are predominantly aligned parallel to the sheet normal. This brings about a poor deformation capability of sheet thinning and a stronger anisotropy and consequently results in a limited number of available plastic deformation modes. In this work, a novel extrusion approach to get high strength magnesium alloy plates will be introduced through differential speed processing. A suitable constitutive model of differential speed extrusion is established to ameliorate the texture -dependent mechanical properties . The velocity evolutions of the extruded sheets at near-surface and mid-layer regions are different due to the extra asymmetric shear deformation . This simple shear enforces the near-surface microstructure to exhibit more dynamically recrystallized grains having the c-axis tilted toward the extrusion direction. The yield stress of AZ31 alloy sheet has been increased from 161.2 to 179.9 MPa, and the elongation has been improved from 15.4 to 20.1%. Moreover, as for the high strength AZ61 alloy sheets, the ultimate tensile strength was increased from 387.9 to 427.1 MPa and the yield stress was improved from 147.7 to 195.9 MPa. Grain refinement and tilted weak basal texture obtained by differential speed extrusion process. This approach is an efficient substitute to increase the texture -induced softening and ductility and thus favorable for the thin sheet fabrication.
