Effect of T6 Treatment on Microstructure and Wear Properties of AlSi10Mg by Selective Laser Melting

Selective laser melting (SLM) technology is an important development in manufacturing. AlSi10Mg is the most widely used aluminum alloy material in the field of SLM. Numerous service properties of the material have been proven to be effectively improved by the T6 (solution + aging) heat treatment, but the effect of T6 heat treatment on the wear behavior of SLM-AlSi10Mg remains unclear. In this study, the dry sliding wear behaviors of stress relieved (SR) and SR+T6 treated SLM-AlSi10Mg at 6, 9, 12 and 15 N were comparatively researched. The results indicated that the microstructure of AlSi precipitates was most affected by the T6 treatment. The volume fraction and average size of the AlSi precipitates increased from 11.4% and 1.28 ± 0.02 μm in the SR treated SLM-AlSi10Mg to 15.5% and 2.13±0.06 μm in the SR+T6 treated SLM-AlSi10Mg, respectively, but its density decreased from 0.084 per square micron of SR treated SLM-AlSi10Mg to 0.040 per square micron of SR+T6 treatedSLM-AlSi10Mg. The weakening of the diffusion strengthening and solid solution strengthening effects reduced the hardness from 104.5HV of SR treated SLM-AlSi10Mg to 86.6HV of SR+T6 treated SLM-AlSi10Mg. The wear resistance of the SR+T6 treated SLM-AlSi10Mg was significantly higher than that of the SR treated SLM-AlSi10Mg at different loading, but with different influencing mechanisms. The increase in loading exacerbated the initiation and propagation of fatigue cracks in the worn subsurface, resulting in a transformation of the main wear mechanism from the micro-cutting (loading of 6 N) to the fatigue spalling (loading of 9, 12 and 15 N). Under the condition of low loading (6 N), the wear resistance of the SR+T6 treated SLM-AlSi10Mg was improved by about 40% compared to the SR treated SLM-AlSi10Mg for the increasing size of AlSi phase. Under the condition of high loading (9, 12 and 15N), the diffusely distributed AlSi precipitates accelerated the formation of the tribology transformed structure (TTS) composed of nano-grains, which in turn aggravated the formation of fatigue crack. As a result, the reduction of AlSi phase density improved the wear resistance of the SR+T6 treated SLM-AlSi10Mg by about 30%~35% compared with the SR treated SLM-AlSi10Mg.