The Influence Of Cr And Sc On The Microstructure And The Mechanical Properties Of Al-cu-mg-ag Alloy

The Al-Cu-Mg-Ag, Al-Cu-Mg-Ag-x Cr and Al-Cu-Mg-Ag-x Sc(for x=0.1, 0.2,0.3, wt.%) alloys were prepared by conventional ingot metallurgy method. The influences of Cr and Sc microalloyed on the microstructure, mechanical property,thermal resistance and corrosion resistance of the Al-Cu-Mg-Ag alloys were investigated by the means of the optical microscopy, scanning electron microscopy,transmission electron microscopy, X-ray diffraction, differential scanning calorimetry,Vicker’s hardness, ambient and elevated temperature tensile, intergranular corrosiond and potentiodynamic polarization text.(1) The Al-Cu-Mg-Ag alloy precipitate dispersed ? and θ? phases, discontinuous grain boundary precipitation and wider precipitation free zone. The Al-Cu-Mg-Ag-x Cr alloys contained 0.3wt.%Cr precipitate the dispersed nano-phase and Al7 Cr particles, and continuous grain boundary precipitation. The Al-Cu-Mg-Ag-x Sc alloy contained 0.3wt.%Sc precipitate the fine and sparse ? and θ? phases, meanwhile,coarse W phase also is precipitated at the grain boundary. And the Al-Cu-Mg-Ag alloy added trace Cr and Sc can decrease the size and density of the residual phases.(2) With the increase of Cr content in the Al-Cu-Mg-Ag-x Cr alloy, the ambient temperature mechanical properties of the alloy strengthen gradually, the tensile and yield strength of the alloy increase from 430 MPa and 374 MPa to 482 MPa and429MPa, respectively. 0.1wt.%Sc has barely effects on the mechanical properties of the alloy, but more Sc contents lead to reducing of the mechanical properties of the Al-Cu-Mg-Ag-x Sc alloy, the tensile and yield strength of the Al-Cu-Mg-Ag-0.3Sc alloy only have 411 MPa and 354 MPa.(3) With the increase of Cr content in the Al-Cu-Mg-Ag-x Cr alloys, the thermal resistance properties of the alloy heighten gradually, the mechanical properties of the alloys’ the elevated temperature tensile at 150~200℃ and the ambient temperature tensile after thermal exposure 100~1000h at 150℃ increase gradually. 0.1wt.%Sc has barely effects on the thermal stability of Al-Cu-Mg-Ag alloy, but when the Sc content in the Al-Cu-Mg-Ag-x Sc alloy continue to grow, the mechanical properties at150~300℃ and after thermal exposure are decreased gradually.(4) With the increase of Cr content in the Al-Cu-Mg-Ag-x Cr alloy, the corrosion resistance properties of the alloy enhance gradually, and that display the maximum depth of corrosion pits in the alloy decrease gradually from 212.3μm to 54.4μm, the self-corrosion potential shift from-0.62232 V to-0.60435 V and the self-corrosion current density also reduce gradually from 2.7358E-6A/cm2 to 2.1497E-6A/cm2. The addition of 0.1wt.%Sc in the Al-Cu-Mg-Ag alloy can improve corrosion resistant properties of the alloy, that exhibit the maximum depth of corrosion pits decrease to91.2μm and self-corrosion potential increase to-0.60070 V, but more Sc contents lead to reducing of the corrosion resistance properties of Al-Cu-Mg-Ag-x Sc alloys, in contrast to the situation of Cr addition, that show the maximum depth of corrosion pits increase to 169.3μm, the self-corrosion potential shift to-0.62485 V, and the self-corrosion current density also rise to 6.0074E-6A/cm2.