Study On Microstructure And Properties Of A356 Aluminum Alloy Cast By 3D Printing Sand Mold

The casting cost is low and the adaptability is wide.It is one of the basic processes in the machinery manufacturing industry.With the rapid development of modern industry,the scale of the foundry market continues to expand,and the requirements for product complexity and manufacturing flexibility are becoming higher and higher.Traditional casting has been unable to meet the market's demand for rapid delivery and highly complex castings.ThreeDimensional Sand Printing(3DSP)technology based on the principle of binder jetting,which does not require mold,can form highly complex structures,and can realize integrated molding of sand molds(cores),has become a current research hot spot in the foundry industry.Almost all studies have been focused on optimizing its sand mold properties and sand structure design.However,few studies focus on the process-microstructure-properties of castings cast by 3D printing sand mold.In this paper,A356 aluminum alloy is used as the study object.Optical microscopy(OM),scanning electron microscopy(SEM),DSC thermal analysis,quantitative metallographic analysis,X-ray inspection and mechanical tensile experiments were used as test methods.The microstructure and mechanical properties of A356 aluminum alloy cast by 3D printing sand mold and traditional resin sand were studied.The effects of sand mold preheating temperature and printing layer thickness on the microstructure and properties of A356 aluminum alloy cast by 3D printing sand mold were systematically studied.The effect of casting thickness on the microstructure and mechanical properties of A356 aluminum alloy cast by 3D printing sand mold was mainly studied.The effect of 3DSP process parameters on the microstructure and properties of A356 aluminum alloy cast by 3D printing sand mold was initially revealed.The main conclusions are as follows:There are no significant differences in the microstructure(secondary dendrite arm spacing of ?-Al,eutectic silicon morphology and size,and type and morphology of Fe-containing phases)of the A356 aluminum alloy samples cast by 3D printing sand mold and traditional resin sand.Whether it is a 3D printing sand casting sample or a traditional resin sand casting sample,there is a certain degree of porosity defects in the alloy structure,which is related to the gas evolution of the resin sand mold.Limited by the working principle of layer-by-layer stacking and no compaction operation,the current standard printing process of 3DSP has a higher amount of binder,so compared with the mature traditional resin sand,the 3DSP sand mold has higher gas evolution.It results that the porosity of 3D printing sand casting samples is slightly higher than traditional resin sand casting samples and the tensile properties are slightly lower than traditional resin sand casting samples.The surface roughness of 3D printed sand castings is lower than traditional resin sand castings.The sand mold preheating temperature(25 ?,100 ?,200 ?)has a significant effect on the microstructure and mechanical properties of A356 aluminum alloy samples cast by 3D printing sand mold.The results show that the microstructure of the alloy coarsens slightly and the tensile properties of the alloy decrease with the increase of the temperature.The alloy has the best properties when cast at 25 ?.The hardness and relative density of the alloy are little affected by the increase of the sand mold preheating temperature and are basically unchanged.When the sand mold preheating temperature is 200 ?,cracks appear on the mold wall after pouring.According to the analysis,high-temperature preheating decomposes the resin bond bridge inside the sand mold and reduces its high temperature mechanical strength.The effect of different printing layer thicknesses(0.3 mm,0.4 mm,0.5 mm)on the properties of A356 aluminum alloy cast by 3D printing sand mold was studied.The results show that within the range of the selected layer thickness,the surface roughness of the casting increases slightly with increasing layer thickness.The surface roughness of the casting was the lowest when the layer thickness was 0.3 mm.It was 11.4 ?m.The tensile properties,hardness and density of the alloy are little affected by the layer thickness.Casting thickness has a significant effect on the microstructure and mechanical properties of A356 aluminum alloy cast by 3D printing sand mold.As the thickness decreases,the secondary dendrite arm spacing of ?-Al,the eutectic silicon size,and the Fe-containing phase size continuously decrease.the porosity defects of the alloy decreased significantly with the decrease of the thickness,and the relative density of the alloy increased significantly.When the thickness decreased from 30 mm to 5 mm,the yield strength,ultimate tensile strength,and elongation of the A356-T6 alloy increased by 16.3 %,33.5 %,826.1 %,respectively.