Fatigue fracture behavior of laser-MIG hybrid welded 7075-T6 aluminium alloys

The influence of stress ratio R and stress range σ_a on the fatigue crack propagation behavior of high strength 7075-T6 aluminum alloy and laser-MIG hybrid welded joint is studied.The results show that under the welding parameters of P=3 000 W, I=110A and v=3 m/min, the fatigue cracking growth rate curve of laser-arc hybrid welding joint intersects with that of base metal.That is due to that the fatigue crack growth rate of hybrid welding joint is lower than that of base metal especially when the SIF range ΔK is less than 15.6 MPa·m^1/2.Under the conditions of same SIF range ΔK, the fatigue cracking growth rate at the higher stress ratio is larger than that of the lower stress ratio.Furthermore, the stress range is more important than the stress ratio(mean stress) to determine the fatigue cracking growth rate of welding joints.