Fatigue Crack Propagation Behavior Of 5052 Aluminum Alloy Joints With Welding Gaps

With the application of aluminum alloy welded components expanding year by year,the fatigue failure of welded joints is becoming more and more serious.Aiming at the problem that the fatigue life of the aluminum alloy welded joint is difficult to meet the service requirements,this paper proposes a method to introduce the unmelted welding gap in the weld center to improve the fatigue performance of the welded joint.The fatigue properties of welded joints were improved by making full use of the hindrance of the crack tip and the optimization of the residual stress of the welded joints.This paper carries on the research through the experimental method.The differences of mechanical properties and fatigue properties between penetration weld joints and non-penetration weld slot joints were compared and analyzed,including the differences of mechanical properties and fatigue properties between weld slot joints of different sizes.The differences of fatigue crack growth performance of each welded joint were obtained by combining the ?-? mechanical property curve,da/d N crack growth rate curve and a-N fatigue life curve.According to the hardness distribution,microstructure and fatigue fracture,the life extension mechanism of joints with welding gaps is revealed.The main research contents and innovative achievements of this paper are as follows:(1)The widely used 5052-H32 aluminum alloy was selected as the research object,and ER5356 was used as the welding wire,and the welding was carried out by artificial non-molten inert gas welding(TIG).According to GB/T985.3-2008 standard,the penetration welding groove was prepared,and the 5052-H32 aluminum alloy was welded.The mechanical properties and fatigue properties of the welded joints were analyzed and tested,and the hardness curve and microstructure of the welded joints were obtained.(2)An innovative process for introducing welding gaps was proposed.Four kinds of welded gap joints,D=1.5mm,D=2mm,D=2.5mm and D=3mm,were prepared.The differences in mechanical properties and fatigue properties of joints with non-penetration welding gaps were compared and analyzed.It is found that the welded joint with D=1.5mm has the best fatigue performance,which accounts for 160.1%,185.2% and 133.5% of the fatigue life of the other three joints,respectively.Meanwhile,the hardness distribution curve of each welded joint is obtained and the fatigue fracture of the welded joint is analyzed.(3)The differences of mechanical properties and fatigue properties between penetration joints and four kinds of joints with non-penetration welding gaps were compared and analyzed.It is found that the fatigue performance of joints with non-penetration welding cracks is much higher than that of joints with penetration welding.The fatigue life of joints with D=1.5mm is 326.6% of the base metal level,and 199.7% of the fatigue level of joints with penetration welding.Based on the hardness distribution,fatigue/tensile fracture and microstructure,the fatigue life extension mechanism of joints with weld gaps was thoroughly analyzed,and the positive effect of introducing cracks in the weld center was explained from two aspects.