Microstructural and Mechanical Properties of a Solid-State Additive Manufactured Magnesium Alloy

Abstract

In recent years, additive manufacturing (AM) has gained prominence in rapid prototyping and production of structural components with complex geometries. Magnesium alloys, which have a strength-to-weight ratio that is superior compared with steel and aluminum alloys, have shown potential in lightweighting applications. However, commercial beam-based AM technologies have limited success with magnesium alloys due to vaporization and hot cracking. Therefore, as an alternative approach, we propose the use of a near net-shape solid-state additive manufacturing process, additive friction stir deposition (AFSD), to fabricate magnesium alloys in bulk. In this study, a parametric investigation was performed to quantify the effect of process parameters on AFSD build quality including volumetric defects and surface quality in magnesium alloy AZ31B. In order to understand the effect of the AFSD process on structural integrity in the magnesium alloy AZ31B, in-depth microstructure and mechanical property characterization was conducted on a bulk AFSD build fabricated with a set of acceptable process parameters. Results of the microstructure analysis of the as-deposited AFSD build revealed bulk microstructure similar to wrought magnesium alloy AZ31 plate. Additionally, similar hardness measurements were found in AFSD build compared with control wrought specimens. While tensile test results of the as-deposited AFSD build exhibited a 20% drop in yield strength (YS), nearly identical ultimate strength was observed compared with the wrought control. The experimental results of this study illustrate the potential of using the AFSD process to additively manufacture Mg alloys for load bearing structural components with achieving wrought-like microstructure and mechanical properties.

Elucidating the Effect of Additive Friction Stir Deposition on the Resulting Microstructure and Mechanical Properties of Magnesium Alloy WE43

“…It should also be noted that Build 12 lacks material mixing between the substrate and the deposit, causing poor layer bonding between successive layers. While not all builds are shown for brevity's sake, cross-sectioned images of all 28 parameters, similar to those shown in Figure 3d-f, revealed that WE43 has a relatively large processing window compared to other AFSD magnesium alloys [22]. Many of the WE43 parameter builds revealed minor macroscopic defects on the surface and galling but were still well consolidated throughout the cross-section.…”

“…An experimental study was performed to identify the appropriate process parameters for WE43. Similar AFSD parameters for Mg Alloy AZ31 reported by Robinson et al were used as an initial baseline for the parametric study [22]. The parametric study varying spindle speed (ω), actuator feed rate (F), and traversing velocity (V) was performed until a well-consolidated build with no surface defects was obtained.…”

“…The deformed material is shaped by the tools path layer-by-layer until the desired component dimensions have been achieved. Each consecutive layer is re-stirred and metallurgically bonded to the previous layer due to the tool geometry described in Avery et al [21] and Robinson et al [22]. The AFSD process has the ability to produce a fully dense build with a refined and homogenous microstructure and exhibit wrought-like mechanical properties in materials such as structural and high-strength aluminum alloys [19][20][21][23][24][25][26][27][28][29][30][31][32][33], magnesium alloys [22], and Inconel alloys [18,34].…”

“…Metals 2021, 11, x FOR PEER REVIEW 3 of 19 [22]. The parametric study varying spindle speed (ω), actuator feed rate (F), and traversing velocity (V) was performed until a well-consolidated build with no surface defects was obtained.…”

“…It should be noted that the parameter study samples will be referred to as Build X, where X is a number 1-28, which correlates to the specific parameters. The hollow AFSD tool used in this study, as dimensioned in Robinson et al [22], is made of H13 tool steel that includes four offset "teardrop" features on the tool shoulder. These features increase the frictional heat and stir previously deposited layers, inducing high shear and severe plastic deformation of the deposited material to metallurgically bond the deposited layers [29].…”