EFFECT of LONG TERM THERMAL EXPOSURE 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. These treatments are typically for only two hours. Longer term exposures are expected to further alter the mechanical properties, however the extent of changes are unknown. In addition, the stress relief thermal treatments can be performed for a range temperatures. The presentation reports the effects of several thermal treatment conditions on mechanical properties of additively manufactured AlSi10Mg.

In this study, specimens of AlSi10Mg were exposed to 200°C, 220°C, 240°C, 260°C, 275°C, and 300°C for various times to characterize the changes in mechanical properties over time. The duration of each isothermal treatment was varied from 15 minutes to 1000 hours; one group of specimens was left in the “As-printed” condition as a control. 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. At all temperatures, the strength decreased while the elongation increased with time. The properties never reached a stable value, as indicated by the change in measurements after 300 and 1000 hours exposure.