Metal Embrittlement

[oldmanandakid]

Is there any general guidance about how long and which metals or Model A components can safely be given the home electrolysis treatment? I am about to put my rear fenders in the soup and don't want to do more harm than good.

 

[bart78]

It will take a long time to eat up good metal. If its just rust you are removing? I like using phosphoric etch and prep. I get it at Home Depot. It will take rust off fast.

 

[Kevin in NJ]

Electrolysis does not eat good iron. It can only remove the red form or rust and reconvert the black oxide back into iron. The surface action can remove some paints and it gets into small spaces better then I expected as it loosened up the bolts at the end of some bumpers.

The process will have trouble with non-steel metals which will loose mass and mess up the anodes.

Because you are created hydrogen at the surface you can cause certain types of hardened and spring metals to become brittle. The low carbon steels used in the sheet metal and wheel will have not problems.

It is important to understand that you must leave the parts in until you get the dark spots at the bottoms of the pits gone. The dark spots hold oxygen and will continue causing rust even after treating with acids or coating with sealing paints.

I have used the Electrolysis to get most of the paint and rust off of wheels cutting my glass beading time in half or more. Since blasting tends to be expensive with materials and energy you stand to save money. It will take longer to do. I also know of people that made large baths with plastic and blocks to do whole sides and bottoms of cars. What you do is limited by your creativity.

 

[MikeK]

You asked about EMBRITTLEMENT, not how much metal will be 'eaten' so I will try to address that. Specifically in ferrous alloys Hydrogen embrittlement occurs when Hydrogen forms at the surface and penetrates the grain boundaries of the alloy. This occurs both in electro cleaning and plating operations. The result is micro expansion of cracks over the next few days. Think of it like water getting into a tiny concrete crack and freezing. The crack opens. Likewise with the metal grain boundaries.

Used parts with micro stress cracks will fare the worst. I would avoid the process on any grade 5 or 8 fasteners, springs, weldments, drive shafts or axles, and suspension components. Used sheet metal that appears OK may develop cracks if flexed, like the fenders in the bead area over the wheel. The hydrogen can be removed after your process by baking the parts @375-400F for about 100 hours (yes, 100!) You need to begin the baking within a few hours of completion of your cleaning process. Extended electrolytic cleaning, in excess of 24 hours may cause unrecoverable damage.

For non-critical parts an acid neutralizing rinse followed by heating the parts to 300F for a few minutes to dry them will be fine.

SAE AMS 2759/9 spells out the procedures for embrittlement relief.

 

[dave in australia]

I'll add a bit more to Kevin's post. Embrittlement occurs when ionic hydrogen is produced at the cathode, the part, during the plating process. Or in this case, the cleaning process. Ionic hydrogen, H1, wants to become gaseous hydrogen, H2, and will combine with another ionic hydrogen atom to do so, becoming H2. H2 is more than twice the size of two individual H1 atoms, so cause internal stresses when they combine. In softer steels, such as panels etc, the metal can accommodate this stress, but higher strength steels can't, so cracks can form. When I was an electroplater, we would carry out a stress relief bake after plating to help prevent cracking.