Alloying And Micro Alloying On Novel Heat-resistant Alloy Used For Automobile Engine Block

To meet the more rigorous requirements of aluminum alloy block for high power density engine working temperature more than 350?,based on the developed Al-12Si-4Cu-1.2Mn alloy,copper as the alloying element is first add to obtain an optimum content of copper in alloy,secondly,nickel is added further to expect to introduce new nickel-rich phase(8-Al3CuNi phase or?-Al7Cu4Ni phase)as new heat-resistent phase in order to improve the strength for 350?.Finally,Erbium and niobium were designed to add into the Al-12Si-4Cu-1.2Mn-1Ni alloy to tailor the microstructure and to improve the high temperature strength.Addition of Cu in Al-12Si-xCu-1.2Mn(x=0,1,2,3,4,5,corresponding to Cu0,Cu1,cu2,Cu3,Cu4,Cu5 alloys)considerably change the solidification process and amount and morphologies of the primary and eutectic Mn-rich strengthening phase.With addition level of Cu,the primary Mn-rich phase gradually changed into coarse dendrites,and the amount of Chinese-script and needle-like Mn-rich phase in two-phases eutectic in Cu0-Cu2 alloys is decreased,and the amount of another Mn-rich phase in two-phases eutectic in Cu3-Cu5alloys is increased and ?(Al2Cu)phase changes from small flocculent into coarse network-like.Among these alloys,Cu4 alloy has excellent high temperature strength,65.1 MPa at 350?,and the fractography of it indicates cracking originates from the primary Mn-rich phase.With addition of Ni in Al-12Si-4Cu-1.2Mn alloy(y= 1,2,3,4,corresponding toNi1,Ni2,Ni3,Ni4 alloys),the amount of the primary Mn-rich phase is increased,however,the amount of Mn-rich phase in two-phases eutectic is decreased and not observed in Ni3-Ni4 alloys as well as?(Al2Cu)phase.New skeleton-like ?-Al3CuNi and blocky ?-Al7Cu4Ni phases are formed in Ni-containing alloys,and rod-like ?-Al3Ni phase is observed in Ni3 and Ni4 alloys.Nil(1wt.%Ni addition)has the highest strength of 97MPa at 350?,of which the fractography indicates cracking originates also from the coarse primary Mn-rich phase,not Ni-rich phases.Microalloying of Er in Al-12Si-4Cu-1.2Mn-1Ni alloy could refine the primary Mn-rich phase,also could change the ?-Al3CuNi phase from skeleton into blocky.It is found that ?(Al2Cu)phases grows adhesively on the newly formed Er-rich phase.Tensile test at 350?suggests that Er addition has no obvious improvementon high temperature strength.Nb-alloying in Al-12Si-4Cu-1.2Mn-1Ni alloy can refine the primary Mn-rich phase,also could change the ?-Al3CuNi phase from skeleton into blocky.It is observed that a new Mn-rich phase of Al50Si30Mn20is formed,however,no Nb-rich phase is observed.Nb-alloyingcould slightly improve the high temperature strength at 350?,=98.8MPa in Nb-1 alloy.