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The 1" of bend you suggest is most likely due to a 'body' rotation and the region where the local bend has occurred may only have been subjected to a relatively small amount of strain but this probably uses up most of the available ductility depending on the alloy.
We have seen several bent arms when they are used on gravel rally cars on very rough surfaces and we have also seen them break with a sufficiently large impact.
I am not sure that there is too much merit in trying to use X-Ray inspection methods as if they have been bent I would be inclined to just replace them.
Annealing Aluminium Castings is really only practical if the alloy is of the Non-Heat Treatable family.
I think that 550degC is a bit on the cool side. There is also the potential that if there is any there is any porosity present in the casting then blistering could occur and this could help produce fatigue initiation sites.
As the alloy is unlikely to be very ductile then the action of straightening the arm will also damage the metallurgical structure and result in a breakage the next time the arm suffers an impact.
If the alloy used is a heat-treatable type then annealing is not really practical as it will tend to overage the alloy and if you manage to create a significantly over-aged structure the arm will lose strength and become brittle due to the precipitates becoming too large.
Over-aging tends to produce 'equilibrium precipitates' that will not respond to solution treatment and will never regain their strengthening effect.
For the costs involved in replacing a bent arm I am not sure that the risk and cost of heat treatment would be worthwhile.
I have never really seen torsion bar brackets bend. I have seen tubes crack and I have seen them bend at the ends where the spring plate covers bolts to the bodyshell.
It would be difficult to rectify this without some form of accurate jig.
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