INVESTIGATION OF POSSIBILITY TO PRODUCE HIGH-STRENGTH BORON ALUMINUM SHEETS WITHOUT HOMOGENIZATION AND QUENCHING OPERATIONS

Al–Cu–Mn (Zr) alloys feature high strength and processability without any thermal treatment operations. Al–2%Cu–1,5%Mn–2%B and Al–2%Cu–1,5%Mn–0,4%Zr–2%B alloys were obtained in order to investigate the possibility of producing a aluminum boroncontaining alloy in the form of high-strength sheet rolled stock without thermal treatment. Melting was performed in the RELTEK induction furnace with intense melt stirring to eliminate sedimentation of boride refractory particles. Melting temperature was 950– 1000 °С. Melt was poured into 40×120×200 mm graphite casting molds. Calculation methods (Thermo-Calc) were used to demonstrate that manganese forms complex borides with aluminum and zirconium at a melting temperature while there is enough manganese in liquid and there is practically no zirconium left. Experimental methods (electronic scanning microscopy and electron microprobe analysis) proved the formation of the complex AlB₂Mn₂ boride, however, manganese remained in a solid solution is enough to form the Al₂₀Cu₂Mn₃ phase particles in the amount up to 7 wt.%. In the alloy with zirconium, boron stimulates primary Al₃Zr crystal separation and, therefore, zirconium content left in the aluminum solid solution is not sufficient for hardening. It is shown that it is possible to produce thin-rolled steel with a thickness of less than 0,3 mm with uniformly distributed clusters of the boride phase with a particle size of less than 10 μm. A high level of strength up to 543 MPa is reached without the use of hardening and aging due to the precipitation of Al₂₀Cu₂Mn₃ phase dispersions during hot deformation (t =450 °C).

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