Effects of Zr additions on structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti (wt.%) alloy

Abstract

Al-Cu-Mg alloys have widespread applications in the aerospace and transportation industries, due to their high specific strength [1] , good oxidation and corrosion resistance, high melting temperature (among Al alloys), and good thermal conductivity [2] . The excellent strength properties of these age-hardenable Al alloys originate from precipitation of the nanoscale metastable phases [1,3,4] , namely θ"-Al 3 Cu with a tetragonal structure (a=0.404 nm and c=0.768 nm), θ'-Al 2 Cu with a tetragonal structure (a=0.404 nm and c=0.580 nm) [3,5,6] , GPB2/S"-Al 10 Cu 3 Mg 3 with an orthorhombic structure (a=0.405 nm, b=1.620 nm and c=0.405 nm) [5,7] , and S'-Al 2 CuMg with an orthorhombic structure (a=0.405 nm, b=0.916 nm and c=0.720 nm) [1,5,6] , in α-Al matrix during age hardening treatments.

Effect of Zr and Ti Addition and Aging Treatment on the Microstructure and Tensile Properties of Al-2%Cu-Based Alloys

“…Thus, it is reasonable to assume that similar reactions will take place in the present alloys. The elongated nature of the Al2Cu particles observed in Figure 15b,d was also observed by Kamali et al [25] in their work.…”

“…The grain refinement in Figure 4b is clearly obtained with 0.3 wt% Zr and comparable to that achieved with 0.15 wt% Ti, as seen in Figure 4c. In addition, in Figure 3c, the average grain size achieved in the 220M alloy (containing 0.3 wt% Zr) is 60 µm, which would indicate that, in the work of Kamali et al [25], the higher cooling rate had a much greater influence on the grain refinement, so the effect of the Zr addition could not be separately discerned. As will be shown further on in Figure 14, the non-dendritic equiaxed nature of the grain structure of alloys G1Z and G3Z (containing 0.15%Zr and 0.3%Zr additions, respectively) is clearly noted, with the G3Z alloy exhibiting a much finer grain structure and virtually no cracks.…”

“…Figure 12 provides the quality index chart of the base alloy with various additions of Zr-Ti for different aging times at aging temperatures of 180 • C and 220 • C. Figure 12a reveals that the G3Z alloy (containing 0.15% Ti and 0.3% Zr) exhibits the highest alloy quality, with a tensile strength of 360 MPa and a Q value of about 415 MPa. Kamali et al [25] also reported that the highest Q value for their T6-heat-treated Al-4.5Cu-0.3 Mg-0.05Ti alloy was observed with a 0.3 wt% Zr addition (249 MPa).…”

“…The strain to fracture is seen to increase for alloys aged at higher temperatures and to decrease with increasing Zr content. Stressstrain curves at 155 °C and 200 °C reveal lower values of peak stress than those at 180 °C, [25] studied the effect of 0.05-0.5 wt% Zr additions on the structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti (wt%) alloy solidified at a high cooling rate (18 • C/s). They reported that the as-cast structure exhibited equiaxed grains of α-Al with an average size of 64 µm, which led them to conclude that the grain size is unaffected by the Zr additions, indicating the ineffectiveness of Zr in the grain refinement of the alloy.…”

“…In their investigations of as-cast and T6-heat-treated Al-4.5Cu-0.3Mg-0.05Ti alloy containing 0.05-0.5 wt% Zr additions, Kamali et al (2022) [25] reported that the highest quality index value was obtained for the T6-treated 0.3 wt% Zr-containing alloy. Quality charts were also used in our study to examine the effects of alloying additions and heat treatment conditions on the resultant tensile properties.…”