Investigation On The Effect Of B On The Microstructure And Property Of Al Heat-resistant Conductive Alloys With Zr Addition By Electrolysis

The heat resistance of the aluminum alloy can be improved by adding appropriate amount of Zr,However,the addition of Zr alloy has a negative effect on the conductivity of the alloy.Studies shows that the adverse effects of Zr on electrical conductivity can be weakened by adding B into the alloy.It is believed that the mechanism of the influence of B addition on the heat conductive properties is different from that of Zr addition.It had been reported that the addition of B in heat-conductive aluminum alloy affects the phase composition and the morphology of Zr,thus weakens the adverse effects on alloy conductivity by the addition of Zr.The effects on microstructure and properties of conductive heat-resistant aluminum alloy containing Zr by adding different content of B were studied in this paper.The results provide useful information for the design and application of the heat-conductive aluminum alloy with Zr both in theoretical and practical aspects.The experimental results are as follows:(1) Controling the addition of B to the heat-resistant aluminum alloy containing Zr below the ratio of B:Zr=2:1,the B and Zr in the alloys form the compound of ZrB₂,ZrB₂ can not be used as the nucleation centers of Al atoms.Therefore it will not play a role in grain refinement,nor increasing the grain boundary.Thus it doesn't have a negative effect on the conductivity of the alloy.Excessive addition of B to alloy containing Zr refine the grain to some extent.However,it might have a negative influence on the conductivity and heat resistance of the alloy.(2) The XRD and SEM results of etching residues of aluminum alloy show that, most Zr exists in a small dispersed floccus phase of Al₃Zr in residue powder sample of non-B alloy,while ZrB₂ particles appear in the samples of alloy containing B.It indicates the addition of B and part of the Zr in the alloy react,form flake-like ZrB₂, existing in the form of second-phase particles.(3) The analysis on the SEM results of as cast aluminum alloy shows that there is no second phase particles containing Zr in the non-B samples.Zr mainly exists as solid solution in the Al matrix,not in the form of second-phase particles.While in the alloy containing B,the second-phase particles containing Zr were observed both in side the grain and at grain boundaries.A large number of second-phase particles containing Zr reunite as a small sheet at grain boundaries.(4) Adding an appropriate amount of B to the heat-resistant aluminum alloy wire containing Zr can increase the tensile strength of the wire,and weaken the negative effect on the conductivity due to Zr addition.However,excessive addition of B would lead to lower conductivity.Hence,the addition of B to the heat-resistant aluminum alloy should be arranged under the ratio of B:Zr=2:1.The aluminum alloy wire achieves the best performance at this specific ratio.(5)The appropriate amount of B,can react with Zr in the alloy,precipitated in the form of ZrB₂,as the second-phase particles,improving the high temperature strength,and the heat-resistant of the alloys.However,the addition of B should be controlled below the ratio of B:Zr=2:1,because the excessive B reduces the high-temperature strength,and the heat resistance of the alloy.