Effect of Stress Relief Treatments on Mechanical Properties of AlSi10Mg

For the additive manufacturing of metals, parts are stress relieved by thermal treatments to reduce internal stresses created by the process. These thermal treatments, while reducing internal stress gradients, can also alter the mechanical properties of the metal. For AlSi10Mg, thermal treatments for stress relief are known to reduce the ultimate tensile strength and yield strength of material, and increase the elongation. What is less well known is the effect of stress relief on other properties. In addition, the stress relief thermal treatments can be performed for a range of times and temperatures, with unknown effects on the mechanical properties. The presentation reports the effects of several thermal treatment conditions on mechanical properties of additively manufactured AlSi10Mg.

In one study, the duration of an isothermal treatment was varied. Specimens were thermally treated at 260°C for 30 minutes, 2 hours, 6 hours, 18 hours, and 54 hours (another group was left in the “As-printed” condition). The resulting microstructure and tensile properties were characterized. Elastic modulus, percent elongation, 0.2% offset yield strength, and ultimate tensile strength were measured and compared. The key difference between groups observed in the microstructure was of the silicon-rich phase. Differences include silicon precipitation from the supersaturated aluminum matrix and cellular network breakdown with increased thermal treatment time.

In a follow on study, the fracture toughness of AlSi10Mg was measured as the temperature of the thermal treatment was varied for two different durations. Fracture toughness specimens were exposed to the following thermal treatment conditions 1) 260°C for 2 hours, 2) 260°C for 6 hours, 3) 275°C for 2 hours, 4) 275°C for 6 hours, and 5) 300°C for 2 hours. One group was left as an “As-printed” control.