Effects Of Rare-earth Modification And Boron Treatment On The Electrical Conductivity Of Al-0.5Mg-0.24Si Alloy

In this paper,Al-0.5Mg-0.24Si alloy taken as the research object,the subject had been carried out from aspects of casting,hot rolling,solution and aging treatment,properties performance and microstructure.The electrical conductivity and tensile strength of aluminum alloy were improved by modification of rare earth and boron treatment.In this paper,the effects of Ce and La additions as well as boron treatment on microstructure and generate the phase morphology,electric conductivity,mechanical properties and corrosion resistancethe metallurgical structure were studied,and the existing form of the added elements had also been discussed which could provide theoretical bases of the reasonable amount of elements addition.The significant results are as follows:(1)With proper addition of rare earth elements(La and Ce),the as-cast microstructure of Al-0.5Mg-0.24Si alloy can be obviously refined,and the morphology of the precipitated phase can be improved.These rare earth elements can react with Si to form Al Re Si compound and Re Si compound,and with Fe to form the Al Re Fe Si compound.Combined with XRD and EDS results,Ce is added to Al-0.5Mg-0.24Si alloy to form Ce₅Si₃and Ce Al_1.2Si_0.8phases with high melting point;The rare earth phase-La Si₂can be formed by adding La to the alloy.However,according to TEM observation,in fact,the Al Re Fe Si phase is composed of rod-like Al₉Fe₂Si₂of different sizes,and the rare earth elements are adsorbed on the surface of the second phase?-Al₉Fe₂Si₂phase.(2)After hot-rolled and heat-treated processes,the improvement of conductivity,tensile strength and corrosion resistance of Al-0.5Mg-0.24Si alloy by adding appropriate amount of Ce is better than that of La additions.Adding the proper amount of rare earth elements,the number of dimples in the tensile fracture structure of the alloy increases and most of them show ductile fracture characteristics,indicating that the ductility of these alloys is improved.When the Ce content is 0.1%,the electrical conductivity of the Al-0.5Mg-0.24Si alloy is 54.42%IACS,the tensile strength is up to 196 MPa,and the elongation after fracture is 17%.Furthermore,the self-corrosion potential of this alloy is positive and the self-corrosion current density is basically unchanged,indicating that the corrosion resistance of this alloy is improved.However,with the addition of 0.3%La,the maximum tensile strength of the alloy merely reaches to 175 MPa,the conductivity is54.05%IACS,the elongation after fracture is 22%,and the corrosion resistance is decreased because of the increase of self-corrosion current density.(3)Boron treatment can obviously reduce the grain size of as-cast Al-0.5Mg-0.24Si alloy.And with the addition of 0.03%B,the average grain size of the alloy can be about680?m.Boron treatment can promote the precipitation of Al Fe Si phase and improves the morphology of the phase.Because boron treatment can reduce the content of transition impurity elements(such as Ti and V)in Al alloy,as the addition of B increases,the electrical conductivity of as-cast aluminum alloy could show a upward trend.After hot-rolled and heat-treated processes,when the B content is 0.04%,the conductivity of the Al alloy is 55.99%IACS,the tensile strength at room temperature is 185MPa,and the elongation after fracture is 20%.Compared with the modification of rare earth,the enhancement of the electrical conductivity and mechanical properties by boron treatment is more significant.This is likely to that due to the difference of the action mechanism between the modification of rare earth and boron treatment.