Effect of Sm + Er and Heat Treatment on As-Cast Microstructure and Mechanical Properties of 7055 Aluminum Alloy

Abstract

The 7055 aluminum alloy is an ultra-high strength aluminum alloy, which is widely used in the aerospace field and new energy automobile manufacturing industry. As it retains high strength, its plastic deformation ability needs to be improved, which limits its application in plastic processing. In this study, the cast grains of the 7055 aluminum alloy were refined by adding Sm + Er, and the proper heat treatment procedure was utilized to further precipitate the rare earth phase in order to increase the alloy’s strength and toughness. The grain size, microstructure and phase were characterized by optical microscopes (OMs), scanning electron microscopy—energy spectrum (SEM-EDS) and a XRD diffractometer (XRD). The macroscopic hardness, yield strength and tensile strength of alloy materials were measured by a hardness meter and universal electronic tensile machine. The results showed that the as-cast sample and the heat treatment sample all contained Al10Cu7Sm2 and Al8Cu4Er rare earth phases. But, after heat treatment, the volume percentage of the rare earth phase dramatically increased and the dispersion was more unified. When 0.3 wt.%Sm and 0.1 wt.%Er were added, the grain size could be refined to 53 μm. With the increase in the total content of rare earth elements, the refining effect first increased and then decreased. Under 410 °C solid solution for 2 h + 150 °C and aging for 12 h, the macroscopic hardness, yield strength, tensile strength and elongation of 0.3 wt.%Sm + 0.1 wt.%Er + 7055 as-cast samples were 155.8 HV, 620.5 MPa, 658.1 MPa and 11.90%, respectively. After the addition of Sm and Er elements and heat treatment, the grain refinement effect of 7055 aluminum alloy was obvious and the plastic property was greatly improved under the premise of maintaining its high-strength advantage.

A Review of the Laser Cladding of Metal-Based Alloys, Ceramic-Reinforced Composites, Amorphous Alloys, and High-Entropy Alloys on Aluminum Alloys

“…Aluminum alloys possess high specific stiffness, high specific strength, excellent corrosion resistance, and easy processability [10][11][12]. It is not only widely used in aerospace, rail transit, shipbuilding, automotive, and military fields, but its development trend is towards larger sizes, integration, complex shapes, and high precision, making it the first choice for lightweight design [12][13][14][15][16][17][18][19][20][21][22].…”

Special Issue: “Advanced Light Metal and Alloys: Preparation, Characterization, and Applications”

“…Studies [1][2][3][4][5][6][7][8] report effects of alloying elements (Sm, Er, In, Bi, Zn, Mg and Cu), preparation technology (cold pressing deformation, annealing, etc.) and microstructure on performance of aluminum alloys.…”

“…Martin-Raya et al [1] discuss the rheological behavior of the A356 aluminum alloy in the semisolid state at low shear rates. Wang and Li [2] report the effect of Sm + Er and heat treatment on as-cast microstructure and mechanical properties of 7055 aluminum alloy. In this study, the cast grains of 7055 aluminum alloy were refined by adding Sm and Er, and the proper heat treatment procedure was utilized to further precipitate the rare earth phase in order to increase the alloy's strength and toughness.…”