Stress relaxation and the cellular structure-dependence of plastic deformation in additively manufactured AlSi10Mg alloys

We investigate and examine the tensile properties and deformation mechanisms of AlSi10Mg alloys fabricated by laser powder-bed-fusion (L-PBF) technology. Repeated stress relaxation experiments were performed to characterize the dependence of activation volume and mobile dislocation density on their intrinsic cellular structures. For the first time, the deformation mechanism of additively manufactured AlSi10Mg alloys was probed by combining these thermal activation analyses with delicate microstructural examinations. A transition in rate-controlling mechanism from a combined effect of solid solution and dislocation forests that formed around cellular boundaries, to conventional precipitate/particle strengthening was proposed, when the continuous cellular structure of the as-printed AlSi10Mg gradually vanished. A model was also developed in collaboration to further understand the deformation physics of additively manufactured AlSi10Mg. Moreover, we found a remarkably improved exhaustion rate of mobile dislocations in AlSi10Mg with continuous cellular structure, which was attributed to a strong work hardening behavior caused by the enhanced accumulation of geometrically necessary dislocations during straining. These cellular structure-related deformation and work hardening mechanisms were primarily interpreted by the different constraint of Si phase on the soft Al matrix. Our results highlight the unique microstructures in additively manufactured metals/alloys that may offer deformation mechanisms substantially distinct from those of their conventional counterparts.