NANO-MECHANICAL CHARACTERIZATION AND CORROSION BEHAVIOUR OF AEROSPACE AL ALLOY

Abstract

Al 5052 alloys are extensively used in aerospace and marine industries due to their high strength to weight ratio and excellence corrosion resistance. Cryo-rolling is one of the important severe deformation processes to produce sheets with high strength. In the present work, The solution-treated Al 5052 alloy was subjected to cryo-rolling(CR) , cryo-groove rolling(CGR) followed by warm rolling (CGW) to a true strain of 2.3 and mechanical and corrosion properties were compared. The deformed samples (90% )thickness reduction) exhibit significant improvement in strength (298 MPa) and hardness (114 HV) in CR samples and 319 MPa and 124 HV in cryo groove rolled samples, which is due to high dislocation density and grain size reduction. The CGR samples rolled at 175 o C shows improved strength (333 MPa) and hardness (133 Hv) with 4.3% ductility, as compared to ST alloy. It was due to the formation of duplex microstructure consisting of both elongated as well as equiaxed sub-grains. Apart from this, the formation of fine precipitates along with deformed or broken impurity phase particles is also responsible for enhancement in tensile strength of CGW samples It is also very essential to understand corrosion behaviour of the materials in addition toensuring superior mechanical properties of the material for its structural application. It is expected that during the process of improving mechanical properties its corrosion behaviourchange with respect to base material. Finer grain size and high volume fraction of grain boundaries in UFG alloys are expected to alter corrosion behaviour, relative to conventional coarse grained (CG) alloys Therefore, an attempt has also been made to evaluate the corrosion behaviour of cryo-rolled Al .The effect of cryrolling on the pitting corrosion resistance of Al5052 alloy was investigated by means of electrochemical polarization technique, in 3.5% NaCl solutions. The difference between Epit-Ecorr of CR, CGR and CGW are more than ST sample which indicates CR and CGR and CGW resulted increased in pitting corrosion resistance of the material. This is due to decrease in the size of impurity precipitates and an increase in the rate of formation of Al oxide films. It is shown that by selecting optimal cryo-rolling reduction result in ultrafine grains in Al 5052 with good combination of high strength ductility and corrosion behaviour. In this study, the effect of thermomechanical treatment on intergranular corrosion (IGC) susceptibility of the different Cryo-rolled samples was investigated.