Effect of Sc on the microstructure and mechanical properties of ZrB2 particles reinforced spray formed 7055 aluminum alloy TIG welded joint

Abstract

Adding nano ceramic particles to the weld seam is an effective way to improve the strength of the spray formed 7055 aluminum alloy welded joint. However, nano ceramic particles are prone to agglomeration, and the agglomerated nano ceramic particles in welded joint can cause stress concentration and brittle fracture of the specimen. In order to improve the aggregation of nano ZrB2 ceramic particles in the weld seam and further improve the mechanical properties of spray formed 7055 aluminum alloy TIG welded joint, Sc/ZrB2-7055 (SZ7) and ZrB2-7055 (Z7) welded joints were prepared in this study. Compared to the Z7 weld seam with coarse grains and severe aggregation of ZrB2 particles, the SZ7 weld seam has fine grains, and the distribution of ZrB2, Al3(Sc, Zr), and Sc modified ZrB2 particles in the weld seam was more uniform. The tensile strength and elongation of Z7 welded joints were 281 MPa and 2.0%, while the tensile strength and elongation of SZ7 welded joints were 320 MPa and 4.9%. The tensile strength and elongation values of SZ7 welded joints have increased by 13.8% and 145% respectively compared to Z7 welded joints. Sc elements formed a rich Sc layer on the surface of ZrB2 particles, which passivated the sharp corners of ZrB2 particles and increased the wettability between ZrB2 particles and Al liquid, resulting in uniform distribution of ZrB2 particles in the weld seams. Fine grain strengthening, dispersion strengthening, and dislocation strengthening are the main reasons for improving the mechanical properties of SZ7 welded joints.

Keywords

• Sc
• ZrB2 particles
• Spray formed 7055 aluminum alloy
• TIG welded joint