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In this research, the effect of several heat treatments on the microstructure and microhardness of TC4 (Ti6Al4V) titanium alloy processed by selective laser melting (SLM) is studied. The results showed that the original acicular martensite α′-phase in the TC4 alloy formed by SLM is converted into a lamellar mixture of α + β for heat treatment temperatures below the critical temperature (T0 at approximately 893 °C). With the increase of heat treatment temperature, the size of the lamellar mixture structure inside of the TC4 part gradually grows. When the heat treatment temperature is above T0, because the cooling rate is relatively steep, the β-phase recrystallization transforms into a compact secondary α-phase, and a basketweave structure can be found because the primary α-phase develop and connect or cross each other with different orientations. The residence time for TC4 SLM parts when the treatment temperature is below the critical temperature has little influence: both the α-phase and the β-phase will tend to coarsen but hinder each other, thereby limiting grain growth. The microhardness gradually decreases with increasing temperature when the TC4 SLM part is treated below the critical temperature. Conversely, the microhardness increases significantly with increasing temperature when the TC4 SLM part is treated above the critical temperature.

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Graphene has been successfully coated with a nano-Al layer through a novel activating treatment (i.e., organic aluminum reduction method). The nano-Al coated graphene was further processed into AlSi10Mg alloy based composites through a selective laser melting (SLM) process. During the nanocoating of Al on graphene, Al atoms deposited on the graphene through organic aluminum reduction gradually, via nucleation and growth process. There were two primary grain growth patterns: two dimensional (2D) layered growth and three dimensional (3D) island growth, until graphene was coated with Al. The Al-coated graphene was added to the AlSi10Mg alloy, refining the cell, increased the tensile strength, hardness and wear resistance of the alloy. Coating Al on the graphene improved the wetting between graphene and Al, and the addition of Al-coated graphene led to a high nucleation rate, which was responsible for refining the cell. This approach facilitated graphene homogeneous distribution in the Al alloy, the interface between graphene and Al was relatively stable, and the grapheme could pin the dislocation and grain boundary. All these attributes enabled superior mechanical properties to be obtained in the final alloy based nanocomposites.