yes, it's extremely difficult to pinpoint defective source material in the supply chain if main supplier has a historically "trusted" supply chain relationship with a wrought aluminum plant which provides rolled sheets or alloy material. not only a metallurgical test and or material analysis via electron microscope is required but also a process inspection is necessary to pinpoint how impurities get in the finished material. my suspicion is improper heat treatment or annealing somewhere has gone wrong especially with aluminum as the base material. you seem to know metallurgy quite well.
SIgh, unfortunately in my business, we deal with China suppliers all the time. Even the so called independent and certified QC companies that many western MNCs use in China, I also don't trust at all. I heard their auditors and inpectors can be bought off by the client, and they then confirm false info to you. I am not an engineer by training, but It can be written into the contract that this testing be done. My understanding from my dealings in that when any metal comes into the SCR Sifang factory for use in their trains, they have to be tested. Whether its steel for the wheels, or aluminum alloy as in this case, it has to be tested to confirm that the supplier shipped them according to the specs required by CSR Sifang. And lets face it, such a large train manufacturer is a major user of metals.
Samples should have been taken when the steel and aluminum rolls come into the factory. LTA should specify access to these samples themselves and conduct independent tests on them. Or at the very lease request to see the CSR test results. Only 3 possible scenarios here.
a) CSR SIfang did no such testing, in which case all their products all over the world are suspect. No one will order from them for such negligence.
b)The samples were tested, but did not meet the metallurgical specs, but CSR ok them for use in the manufacture. Either someone was bribed to accept them or some hanky panky going on.
c) CSR tested them, found that the batch was unacceptable, but decided to accept them anyway because of time constraints. THey might then have falsified the tests to make it look as though the batch was acceptable for use.