modeling and optimizing creep behavior of a356 al alloy in presence of nickel using response surface method

The present paper aims to model the creep behavior of a356 al alloy in the presence of different amounts of nickel and evaluate the microstructure of the alloys using optical microscope and scanning electron microscope (sem). creep properties of the alloys were obtained using the impression creep method by a cylindrical indenter within the stress range of 0.027<σ/g<0.030 at 473-513k. as indicated by the results, adding nickel to a356 alloy would result in eliminating the harmful phases of iron, modifying the morphology of α-al dendrites, and creating new nickelrich phases, besides improving the creep strength of the alloy. this is due to the formation of nickelrich intermetallic compounds and prevention from the formation of iron-rich phases. by calculating the creep activation energy and stress power, it was found that the climb-controlled dislocation creep in the dominant mechanism network in the creep deformation of a356 alloy was in the cast state and under the studied conditions. also, nickel had no effect on the creep mechanism. besides, the equation of the creep deformation of the alloys (the relationship between temperature, stress, and stable-state creep strain rate) was obtained. this equation can be used to predict the stablestate creep strain rate at certain temperature and stress for a356 alloy and nickel-containing alloys under climb controlled dislocation creep conditions.