Artifitial Aging Time Effect on Corrosion Resistance for Friction Stir Welded AA6061 T6

Abstract

This work aims to study the effect of heat treatment on the corrosion resistance of friction stir welded joint of AA 6061 T6.Friction stir welding process carried out using CNC milling machine with a tool of rotational speed (1000 rpm) and welding speed of (20mm/min) to obtain butt joint welding of sheets which prepared from AA 6061 T6 in the dimensions of (100 mm x 70mm x 6mm ).After obtaining the welded joints many corrosion specimens were prepared in dimensions of (15*15*2) mm according to ASTM G 71-31 , specimens subjected to solution heat treatment at 500ºC for half an hour then water quenched, this process followed by artificial ageing at 190ºC for 2, 4, and 6hrs.All specimens subjected to hardness test and microstructure examination to show the effect of the heat treatment on the mechanical properties and microstructure.Corrosion behavior of the specimens were studied before and after heat treatment by using potentiostatic method in sea water at 3.5%NaCl and temperature of 30ºC, then corrosion rate was calculated by using Tafel equation.The obtained results show that artificial aging treatment contributed in increasing the corrosion resistance of weld because of presence of precipitate phases occurring in the microstructures of the welding zone but corrosion resistance decreased as increasing ageing time because of the increasing of the precipitating elements. It was found that artificial ageing for 2 hours gives the best corrosion resistance.