Chemical Composition Effect on Microstructures and Mechanical Properties in Friction Stir Additive Manufacturing

The variation of chemical compositions can affect the mechanical property of friction stir additive manufacturing(FSAM).Quantitative characterization of the relationship between the chemical composition and the mechanical property of FSAM components is key to control the quality of FSAM components.The effect of chemical composition on the mechanical property of 6 xxx series aluminum alloy FSAM joint was studied by both experimental and numerical methods.A moving heat source model was established to simulate the heat transfer in FSAM process.The average grain size was calculated by Monte Carlo model,and the precipitate evolution model was used to calculate the hardness and constitutive stress-strain relationship.The validity of the numerical model was verified by experiments.Results indicate that the hardness and yield stress of 6 xxx series aluminum alloy FSAW joint can be enhanced by increasing silicon or magnesium contents.By increasing the content of magnesium(silicon),the volume fraction and the mean radius of MgSi can be increased when the content of silicon(magnesium) is excessive.With the decrease in volume fraction,the average grain size can be increased.By changing the weight percentage of magnesium and silicon in different layers,the hardness and yield stress along the build direction can be controlled.