What lives in washing machines and eats aluminium alloy?

[marcophys]

The washing machine stopped spinning, so I dismantled it.
Here's what I found:



I'm thinking it might have become a big battery, as the steel drive shaft was embedded in the alloy drive bracket, which in turn had 6 studs bolting it to the stainless steel drum.
It was all enclosed in the sealed water drum.

What I find interesting is the extent of the disintegration.
Also interesting is the design failure.

 

[Borek]

Electrolytic corrosion sound plausible. Add high temperatures, high concentrations of ions (increasing water conductivity) and alkaline conditions (typical in many washing powder recipes) and it is a disaster waiting to happen.

 

[ebos]

Add in the 'cheapness' factor...

 

[marcophys]

Add in the 'cheapness' factor...

Or perhaps it was designed to fail.

 

[diogenesNY]

You might want to try to get a report on the local water chemistry. (This is probably available from some town/county agency or somesuch). Dissolved minerals, gas content, &c could be playing a meaningful role in facilitating this process.

diogenesNY

 

[dschlink]

Completely normal for aluminum bolted to steel. The corrosion is concentrated along grain edges, so the aluminum disintegrates. I saw a lot of this working in the cable industry along the California coast. The cases for amplifiers were aluminum and the connectors steel. After a couple years in the salt spray, the case would fall apart when you tried to remove a connector.

I think I recognize the washing machine. A friend had one fail like that and the hub was caked with residue from the powdered detergent she used.

 

[strangerep]

Completely normal for aluminum bolted to steel.

Yeah -- isn't this just a standard case of what happens if you join dissimilar metals? I.e., according to the Galvanic series. The aluminium needs to be electrically isolated from the steel somehow. Sometimes plastic washers can help. There's also some paint-on goop available in marine supply stores, intended for essentially the same problem in boats, where you often want to use SS fasteners between Al sections.