Corrosion Properties of Laser Welded Superaustenitic Stainless Steel Sandwich Structures

Cellular metal sandwich panels are ideal for blast resistant structures due to favorable thermal management and energy absorbing capabilities. Structures that experience exposure in marine environments may be constructed using intrinsically corrosion resistant superaustenitic stainless steel such as AL-6XN (UNS N08367 20.5%Cr-6.2%Mo-0.24%N by weight). However, cellular structures contain occluded sites at metallurgically altered nodes attaching face sheets and cores depending on the joining strategy. One possible joining method is by autogenous laser welding, which offers rapid cooling and a high degree of precision over welding parameters. Increased weld input energy, while favorable for bonding, can lower the weld region corrosion resistance through segregation of alloying elements and by the increasing dimensions of Mo-lean dendritic regions. A series of autogenous laser spot welds was prepared on both a 1.3 mm thick sheet of AL-6XN and 1.4 mm thick coupons of 316L (UNS S31603 17%Cr-2.5%Mo) alloy. Test coupons were prepared over a wide range of weld parameters to simulate the range of industrial parameters that could be encountered in sandwich structure construction. Electrochemical corrosion studies are being carried out both at the macro and micro scales on weld samples to elucidate the effect of various weld parameters on crevice corrosion behavior.