Pinless friction stir welding of AA2024-T3 joint and its failure modes

Abstract

The joining of aluminum alloy sheets with thickness less than 2.0 mm is difficult via conventional friction stir welding owing to the defects in the joint, such as root flaw, keyhole and lazy S. In the present research, a newly designed pinless tool with involute grooves on its shoulder surface was applied to weld 1.5 mm thick AA2024-T3. The effects of the rotating speed and welding speed on the microstructure and mechanical properties of the joints were analyzed. The experimental results showed that the root flaw and keyhole were successfully eliminated. The lazy S was also eliminated under the optimized welding parameters. The maximum tensile strength of the joints was 326 MPa, which is about 74.1% that of the base material. Moreover, all the tensile samples fractured from the retreating side. Two fracture modes were observed during the tensile tests, which are related with the lazy S.

Keywords

pinless friction stir welding / AA2024-T3 / mechanical property / fracture mode

References

[1] Thomas W M, Nicholas E D, Needham J C, et al. Friction Stir Welding[P]. 1991

[2] Mishra R S, Ma Z Y. Friction stir welding and processing[ J]. Materials Science & Engineering R: Reports, 2005, 50(1/2): 1-78.

[3] Nandan R, DebRoy T, Bhadeshia H K D H. Recent advances in friction-stir welding — Process, weldment structure and properties[J]. Progress in Materials Science, 2008, 53(6): 980-1023.

[4] Zhou C, Yang X, Luan Guohong. Effect of root flaws on the fatigue property of friction stir welds in 2024-T3 aluminum alloys[J]. Materials Science and Engineering A, 2006, 418(1/2): 155-160.

[5] Chen H, Yan K, Lin T, et al. The investigation of typical welding defects for 5456 aluminum alloy friction stir welds[J]. Materials Science and Engineering A, 2006, 433(1/2): 64-69.

[6] Dickerson T L, Przydatek J. Fatigue of friction stir welds in aluminium alloys that contain root flaws[J]. International Journal of Fatigue, 2003, 25(12): 1399-1409.

[7] Okamoto K, Sato A, Park S H, et al. Microstructure and mechanical properties of FSWed aluminum extrusion with bobbin tools[J]. Materials Science Forum, 2012, 706–709, 990-995.

[8] Barlas Z, Ozsarac U. Effects of FSW parameters on joint properties of AlMg3 alloy[J]. Welding Journal, 2012, 91(1): 16S-22S.

[9] Wanjara P, Monsarrat B, Larose S. Gap tolerance allowance and robotic operational window for friction stir butt welding of AA6061[J]. Journal of Materials Processing Technology, 2013, 213(4): 631-640.

[10] Bakavos D, Prangnell P B. Effect of reduced or zero pin length and anvil insulation on friction stir spot welding thin gauge 6111 automotive sheet[J]. Science and Technology of Welding and Joining, 2009, 14(5): 443-456.

[11] Wang W B, Li G, Luo G H, et al. Flowing Friction Welding Method and Tool[P]. CN Patent Application No. 200910238020. 1, 2009

[12] Forcellese A, Gabrielli F, Simoncini M. Mechanical properties and microstructure of joints in AZ31 thin sheets obtained by friction stir welding using “pin” and “pinless” tool configurations[J]. Materials and Design, 2012, 34, 219-229.

[13] Forcellese A, Simoncini M. Plastic flow behaviour and formability of friction stir welded joints in AZ31 thin sheets obtained using the “pinless” tool configuration[J]. Materials and Design, 2012, 36, 123-129.

[14] Simoncini M, Forcellese A. Effect of the welding parameters and tool configuration on micro- and macromechanical properties of similar and dissimilar FSWed joints in AA5754 and AZ31 thin sheets[J]. Materials and Design, 2012, 41, 50-60.