Need Help!- Aluminum Staining

[337MPH]

Hey guys so been running parts in our new Mazak and we run our normal coolant trim e206 run it in the rest of the machines and we run a part and it comes out shiny then it goes and get solvent washed heated with a oxy acet torch gets parts installed then comes back to the machine and gets finish work done

now whats happening is it goes in and is machined for about 4 1/2 hrs they go in perfect really shiny then they come out with a brownish tint to them we thought it was the oil in the sump cause they didnt clean the machine when it showed up so all the cosmoline was still on the covers and ended up in the tank

so it got completely cleaned and wiped down new coolant agian 10% mix also useing Deionized water still stained

so started checking PH was low so we brought it up still doin it, didnt heat them they came out perfect no stain so it must be the heating of them

what makes it odd is why does it do it in this machine and not the machine they used to get run it which is and old Bostomatic. so i realized is the torch heating them thats doin is so im guessing its cause of the carbon and oxygen from it and something is making it show up in the aluminum anyone have any ideas? or had this issue

the material is 6013 aluminum

Thanks
JM