Study On The Control Mechanism Of Al-Ce Phase In AZ80-2Sn-2Ce Magnesium Alloy

AZ magnesium alloy is the most widely used magnesium alloy.It has the advantages of good casting performance,low cost and wide application range.However,its mechanical properties are still far from the other alloys,which limits the application range of AZ magnesium alloy to a certain extent.,Therefore,improving the mechanical properties of AZ magnesium alloys is of great significance for the wider application of AZ magnesium alloys.Based on the previous research of this group,AZ80-2Sn-2Ce magnesium alloy was selected as the research object.XRD,DSC,EDS,SEM and FESEM were used to analyze the Al-Ce phase in the magnesium alloy.It is expected to improve the as-cast microstructure of the alloy by controlling the morphology,size and distribution of the Al-Ce phase,thereby improving the mechanical properties of the alloy.This paper first analyzes the effect of melt sonication on the Al-Ce phase in the experimental alloy.The results show that the alloy structure is mainly composed of?-Mg,Mg17Al12,Al₄Ce and a small amount of Mg₂Sn phase.In the alloy structure without ultrasonic treatment,the morphology of the Al₄Ce phase begins to be granular.As time goes on,some of the earlier nucleated Al₄Ce phases grow into needle-like shape,which continues to grow with the Al₄Ce phase.In the alloy structure,a part of the acicular Al₄Ce phase is transformed into a tubular morphology.When the ultrasonic power is 300W,the Al₄Ce phase structure in the alloy has a small amount of tubular shape.When the ultrasonic power is 500W,the number of bulk Al₄Ce phases increases,and only a small amount of tubular Al₄Ce phase in the structure,when the ultrasonic power is 700W,The size of the bulk Al₄Ce phase becomes more coarse.The results show that:there are three main factors that cause these phenomena.First,because the crystal structure of Al₄Ce phase is a body-centered tetragonal structure,the growth rate of crystals at different interfaces is different,while the?001?crystal plane of Al₄Ce is non-closed surface makes the crystal attract the strongest attraction to the Al and Ce atoms,and finally the Al₄Ce crystal has the fastest growth rate in the direction perpendicular to the?001?crystal plane.In addition,As the crystal size of Al₄Ce increases,the diffusion capacity of Al and Ce atoms at the edge of the crystal to the center of the crystal is weakened,resulting in the center of the crystal in a state of depleted Al and Ce atoms.In addition,the Sn element is enriched in the hollow position of the Al₄Ce phase,and the formation of the constitutional supercooling,which further limits the growth at the center of the Al₄Ce phase..The two together work to stop the growth at the center of the crystal and form a hollow,which makes the Al₄Ce phase grow into a tubular shape.Second,when sonicating the test alloy melt,cavitation and acoustic flow effects are generated in the alloy melt.The cavitation effect causes a strong shock wave to form in the melt,causing the needle-like and tubular Al₄Ce phases in the alloy to break up to form a granular Al₄Ce phase.The acoustic flow effect will agitate the melt and enhance the diffusion capacity of Al and Ce atoms in the melt,so that the Al and Ce atoms at the edge of the Al₄Ce crystal are more likely to diffuse toward the center.Therefore,after sonication,the needle-like and tubular Al₄Ce phases in the alloy are transformed into a block shape.Third,due to the thermal effect of ultrasonic treatment,the cooling rate of the alloy decreases,and as the ultrasonic power increases,the thermal effect in the alloy melt is more obvious.Therefore,when the ultrasonic power is 700 W,the cooling rate of the melt is the slowest,increasing the growth time of the Al₄Ce phase,so the Al₄Ce phase is the most coarse when the ultrasonic power is 700W.In addition,the size of the Al₄Ce phase in the test alloy varies.The study shows that this is because the Al₄Ce phase is a high temperature phase?the melting point is1235°C?.As the cooled Al₄Ce phase of the test alloy continues to nucleate and grow in the melt,previously the nucleated Al₄Ce phase has a longer growth time and a faster growth rate,making it larger in size.The later nucleated Al₄Ce phase is smaller in size due to the shorter consumption of the Al and Ce atoms and growth time.Comparing the microstructure and mechanical properties of alloys after applying different ultrasonic powers,it is found that the change of Al₄Ce phase in the alloy has a significant effect on the mechanical properties of the test alloy.Due to the cavitation effect of ultrasonic treatment,the acicular and tubular Al₄Ce phase in the alloy is broken.The nucleation core of the Al₄Ce phase is increased,and more Al₄Ce phase is formed in the alloy,thereby increasing the tensile strength and yield strength of the alloy and reducing the elongation of the alloy.However,due to the thermal effect of the ultrasonic treatment,When the ultrasonic power is 500 and 700W,the size of Al₄Ce in the alloy is larger than that at 300W,which deteriorates the mechanical properties of the alloy.Then the effect of solidification rate on the morphology and size of Al-Ce phase in the test alloy was preliminarily analyzed.It is found that the faster the solidification rate,the more Al-Ce phase in the alloy is needle-like and the smaller the size,the slower the solidification rate,the larger the number of tubular Al-Ce phases in the alloy and the larger the size,because When the velocity increases,the Al,Sn and Ce elements in the alloy are too late to precipitate,and the alloy melt has solidified,which reduces the nucleation growth time of the Al4Ce phase,resulting in the formation of a needle-like morphology and a small size of the Al₄Ce phase.