摘要
As-cast Al-Si alloys always face low ductility because of coarseα-Al grains and large lamellar eutectic Si.Although B-containing refiners and Sr modifiers could refine theα-Al grains and eutectic Si respec-tively,simultaneous addition leads to an invalid effect of Sr because B-containing refiner has a poison-ing effect(PE)on Sr modifier in the Al-10Si-B-Sr alloys.The present work achieves both refinement ofα-Al grains and modification of Si merely by the addition of 500 ppm La in Al-10Si-0.02B-0.015Sr alloy,which greatly enhances the ductility and tensile strength.Sr-B interaction in the Al-10Si-0.02B-0.015Sr melt results in a consumption of Sr by forming Sr-B intermetallic compound.CALPHAD-type calculations reveal that Sr concentration in liquid before eutectic reaction becomes a key parameter to estimate the alloying modification effect.The addition of La forms LaB 6 and thereby releases Sr to protect the Sr modification effect.First-principles calculations illustrate that both Sr and La are benefi-cial to the formation of twin boundaries in Si particles due to their negative formation energy of twin boundaries.The formed LaB 6 has a semicoherent interface withα-Al with the orientation relationship of[110]_(LaB6)//[110]_(Al) and(111)_(LaB6)//(111)_(Al),demonstrating that LaB 6 is an efficient nucleation site forα-Al,which contributes to the refinement ofα-Al in the Al-10Si-0.05La-0.02B-0.015Sr alloy.Our findings re-veal the micro-mechanism of refinement during the solidification process and develop an effective and simple way to obtain high-performance Al alloys.
基金
This work was financially supported by the National Natural Science Foundation of China(Nos.U2102212,51871138,and 51821001)
the Shanghai Rising-Star Program(No.21QA1403200)
the Shanghai Engineering Research Center for Metal Parts Green Remanufacture(No.19DZ2252900)from Shanghai Engineering Research Center Construction Project.
