Hello researchers,
Can anyone please explain the effects of shrinkage cavity/voids on the mechanical properties of resistance spot welded advanced high strength steels? I could find some journals of the shrinkage cavity in castings, but not resistance spot welding. If possible, please provide me some articles also in the same issue.
Thanking You and best regards
Siva Prasad Murugan
It is natural that this discussion should centre on the effect of porosity. Clearly, porosity in a weld reduces the area to support stress, plus there may be some geometrical stress enhancement to some degree.
However, it is helpful to bear in mind that it is highly probable, if not certain, that the porosity formed from the expansion of gases trapped within a bifilm. The heat and sudden reduction of constraint on an entrained double oxide film floating about in the weld pool may create visible pores, but far more importantly, the bifilm itself will act as a crack, usually taking up a far larger area than the visible pore. Unfortunately, bifilms are generally only nanometres in thickness, and so difficult to detect.
In those welding processes in which cracking in the heat affected zone (HAZ) is common, in my experience this is always the result of the poor casting technology used to cast the steel. If the steel were cast without the entrainment of air during pouring, it would be relatively free from bifilm cracks, and would not subsequently form HAZ cracks.
I tend to find that those working in welding research have so far generally overlooked the potential of bifilms to create many of the problems suffered in welding. For a complete review of bifilms, their formation and avoidance, in metals of all types, including steels, I recommend my "Complete Casting Handbook" 2nd Edition 2015.
Best of luck with your research.
John Campbell
Dear Siva, Resistance welding is done as spot welding and today's technology is such that the weld nugget size and area are so small and since pressure is also applied during resistance spot welding, I donot think there is a possibility for a large weld pool for shrinkage to appear. Even if some small shrink spots are there is no possibility of AHSS steels strength to get affected. Shall let you know if I get further information on this. Good Luck A.V.Sethuraman
It is natural that this discussion should centre on the effect of porosity. Clearly, porosity in a weld reduces the area to support stress, plus there may be some geometrical stress enhancement to some degree.
However, it is helpful to bear in mind that it is highly probable, if not certain, that the porosity formed from the expansion of gases trapped within a bifilm. The heat and sudden reduction of constraint on an entrained double oxide film floating about in the weld pool may create visible pores, but far more importantly, the bifilm itself will act as a crack, usually taking up a far larger area than the visible pore. Unfortunately, bifilms are generally only nanometres in thickness, and so difficult to detect.
In those welding processes in which cracking in the heat affected zone (HAZ) is common, in my experience this is always the result of the poor casting technology used to cast the steel. If the steel were cast without the entrainment of air during pouring, it would be relatively free from bifilm cracks, and would not subsequently form HAZ cracks.
I tend to find that those working in welding research have so far generally overlooked the potential of bifilms to create many of the problems suffered in welding. For a complete review of bifilms, their formation and avoidance, in metals of all types, including steels, I recommend my "Complete Casting Handbook" 2nd Edition 2015.
Best of luck with your research.
John Campbell
@ Prof. John Campbell, Prof. Adachani Viswanathan Sethuraman, Prof A. M. Al-Mukhtar .... Thank you for your valuable comments on the issue.
Simply, during any loading, stresses will be concentrated on the formed porosities that have a lesser resistance thus leading to a strain localization (heterogeneous deformation) which will ultimately result in the material failure.
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