In reply to JJL:
I really doubt that even DMM would perform grain boundary inspection on 50mm aluminium bar stock.
You might expect someone in the nuclear or aerospace industry, that have anally paranoid QC/QA departments to do so.
For the majority of consumers, the Certificate of Conformity provided by the manufacturer is guarantee enough.
The whole point to a certificate of conformity is that the consumer does not have to repeat tests that the manufacturer should already be doing as part of their own QC/QA process.
Most testing done by a manufacturer is done on the components that they produce rather than the raw materials, and if the cracking is something that develops over time, then even 100% testing would probably have failed to spot it.
This appears to be something that has slipped through the manufacturers QC procedures for whatever reason, slipped through DMM's because they trusted the supplier, and been discovered after the product had been sold, at which point the fault was still undetectable by the usual QC procedures employed by DMM.
Even after something like this I still wouldn't expect DMM to do grain boundary analysis on goods inwards, but I would expect them to ask the manufacturer to do it, and provide the results, for a reasonable period of time following this incident.