Joining 6061 aluminum alloy with Al–Si–Cu filler metals

In this study, brazing of 6061 aluminum alloy was carried out with Al–10.8Si–10Cu and Al–9.6Si–20Cu filler metals at 560 °C. The addition of 10 wt.% copper into the Al–12Si filler metal lowered the solidus temperature from 586 °C to 522 °C, and the liquidus temperature from 592 °C to 570 °C. With the addition of 20 wt.% copper into the Al–12Si filler metal, the liquidus temperature of the filler metals decreased from 592 °C to 535 °C. The main microstructures of the two Al–Si–Cu filler metals in the study consisted of Al solid solution, fine silicon particles, and Al2Cu intermetallic compounds. The shear strengths of the 6061 alloy brazed with Al–12Si at 600 °C decreased as brazing time increased. The average shear strengths fell from 39 MPa for 10 min to 23 MPa for 60 min of brazing. Joint strengths of the 6061 alloy brazed with Al–10.8Si–10Cu filler metal increased as brazing time increased and reached about 67 MPa at the brazing time of 60 min. Shear strengths of about 40 MPa for the 6061 aluminum joint with Al–9.6Si–20Cu filler metal were obtained irrespective of the brazing periods. The high hardness value of the 6061 aluminum alloy subtract near the butt joint interface after brazing with Al–Si–Cu filler metal could be attributed to the fact that the copper penetrated and formed Al2Cu intermetallic compounds.