Effect of Diffusion Bonding on Fatigue Strength of Aluminum Alloy AA 7020-O

Abstract

The aim of this research is to study the fatigue behavior of aluminum alloyAA7020-O joining by diffusion welding with simple self pressurizing fixture inmuffle furnace. This alloy was bonded by using different variables; pressure,temperature and time. The maximum shear strength of diffusion bonded was 76MPa at pressure 15 MPa, 500 ºC and 20 min. The moderate shear strength was dueto the presence of small amount of Mg (1%) which acts as deoxidizer element andallows the atoms to cross the interface. New intermetallic compounds;All3Mg3Zn3, Al18Mg3Cr2 were formed during diffusion and Al3Zr wasdisappeared. Diffusivity (D), average depth of diffusion and activation energy (Q)was calculated from the depletion area and they were 3.1 × 10 -9 cm2 / sec, 19.3μmand 2062 KJ/Kg respectively. From the S/N curve of fatigue test, the life of thebonded specimens were less about 60 to 70% comparing with unboundedspecimens. The fatigue strength for AA7020-O is equal to 77 MPa at 107 cycles,while the fatigue strength reduces to 29 MPa at 107 cycles for diffusion specimens.So, diffusion interface can be considered asa notch and the crack initiation stagehas been achieved and the failure of the diffusion specimens started from thepropagation stage.