A Study On Selective Laser Melting Of AlSi10Mg Alloy And AlSi10Mg-SiC_p Composite

Selective laser melting?SLM?,as one of the most important additive manufacturing techniques for metals,has been widely used for aluminum alloys,especially for AlSi10Mg.In this study,two types of AlSi10Mg powder with different particle size distributions and powder morphologies were used for final density comparison upon SLM processing in order to investigate the effect of powder properties on final density.One of the AlSi10Mg powders with better densification behavior was selected for a design of experiment?DOE?based on Box-Behnken response surface methodology to establish a model between SLM processing parameters and SLM processed density.The comparison investigation was made on the SLM processing parameters for AlSi10Mg alloy and AlSi10Mg-SiC_p composite with 5 vol.%SiC in order to explore the effect of SiC particle on the densification behavior of AlSi10Mg alloy matrix.A model of SLM processing parameters vs.final density of AlSi10Mg-SiC_p composite was established using Box-Behnken response surface design.A comprehensive investigation was made on the effects of SLM processing and T5 heat treatment on the microstructure and mechanical behavior of both AlSi10Mg alloy and AlSi10Mg-SiC_p composite.It was found that:?1?The particle size distribution of AlSi10Mg powder has a critical effect on the densification behavior upon SLM processing.The higher content of coarser particle results in the higher SLM processed density.?2?The relationship model between relative density?RD?of SLM processed AlSi10Mg alloy and SLM processing parameters,including laser power?P,W?,scanning speed?S,mm/s?,and hatch space?D,?m?,has been established using Box-Behnken response surface design and can be expressed as:RD=0.4885+0.0034P-0.0002S+0.0018D+6.38×10^-7PS+5.86×10^-6PD-7.76×10^-7SD-5.97×10^-6P²-6.10×10^-9S²+1.17×10^-5D²The model shows that the maximum relative density of 98.3%can be achieved using optimal SLM processing parameters of laser power 375 W,scanning speed 2000 mm/s,and hatch space 50?m.Due to the addition of 5 vol.%SiC,the optimum SLM processing for AlSi10Mg cannot yield a good density for AlSi10Mg-5 vol.%SiC_p composite.By using Box-Behnken response surface design again,this study shows the relationship model between relative density?RD?of SLM processed AlSi10Mg-5 vol.%SiC_p composite and SLM processing parameters of laser power P,W;scanning speed S,mm/s;and hatch space D,?m;can be expressed as:RD=2.61-0.0224P-0.0059S+0.0105D+8.93×10^-5PS+8.63×10^-6PD-3.10×10^-5SD+5.51×10^-5P²-4.69×10^-6S²-8.59×10^-5D²-2.15×10^-8P²SThe corresponding optimum SLM processing parameters per this model include laser power 240 W,scanning speed 245 mm/s,and hatch space 26.2?m for the maximum relative density of 97.1%.?3?Optical microscope analysis shows that there are significant anisotropic microstructures for both SLM processed AlSi10Mg and AlSi10Mg-5 vol.%SiC_p composite.The cladding zone size in vertical cross section?parallel to the laser direction?of the SLM processed samples is significantly smaller than that in parallel cross section?vertical to the laser direction?.The cladding line density in vertical cross section is much higher than that in horizontal cross section.And the hardness in vertical cross section is significantly lower than that in horizontal cross section;SEM analysis shows that before any heat treatment,both AlSi10Mg alloy and AlSi10Mg-5 vol.%SiC_p composite are composed ofa-Al cell surround with thin regions of either Al-Si eutectic structure?for AlSi10Mg alloy?or the mixture of Al-Si eutectic structure and SiC particles?for AlSi10Mg-5 vol.%SiC_p composite?.For AlSi10Mg-5 vol.%SiC_p composite,the SiC particles is always mixed with Al-Si eutectic structure except some SiC clustering regions.T5 heat treatment significantly diminishes the cladding zones of both AlSi10Mg alloy and AlSi10Mg-5 vol.%SiC_p composite.At the same time,T5 heat treatment results in the significant growth of Si particles.And the Si particle distribution becomes more homogenously ina-Al matrix and thus thea-Al cell structure before heat treatment disappears.Consequently,the anisotropy of microstructure and mechanical properties for both AlSi10Mg alloy and AlSi10Mg-5 vol.%SiC_p composite is significantly reduced upon T5 heat treatment.?4?T5 heat treatment significantly reduces the hardness of both AlSi10Mg alloy and AlSi10Mg-5 vol.%SiC_p composite.The hardness of AlSi10Mg-5 vol.%SiC_p composite is always higher than that of AlSi10Mg alloy before and after heat treatment.Tensile test shows that before heat treatment,the UTSs for AlSi10Mg and AlSi10Mg-5 vol.%SiC_p composite are 468 MPa and 495 MPa respectively and the elongations for AlSi10Mg and AlSi10Mg-5 vol.%SiC_p composite are 8.3%and 3.7%respectively.And after heat treatment,the UTSs for AlSi10Mg and AlSi10Mg-5 vol.%SiC_p composite are 207 MPa and 317 MPa respectively and the elongations for AlSi10Mg and AlSi10Mg-5 vol.%SiC_p composite are 19.2%and 4.2%respectively.