The meaning of each character is the same. They both signify a range of acceptable dimensions (from 0.025 mm to 1.00 mm, from 1.00 mm to 2.25 mm). SAE does not adhere to stringent format rules for their standards, so you can see many examples like this when using their standards.
This is bainite microstructure, and based on low toughness, it must be upper bainite. This structure is possible with 4140 steel when it has been subjected to intermediate cooling from the austenite phase.
TL 211 is a standard from Volkswagen, with the title Paint Coating on Exterior Plastic Parts.
PV 1200 is another standard from Volkswagen, with the title Aggregate, Bauelemente, Systeme, Halbzeuge - Klimawechseltest.
You can contact VW for more information.
Welds typically are fatigue sensitive. The best weld FEA that I know is Verity from Battelle:
http://www.battelle.org/our-work/consumer-industrial/battelle-verity
Verity can be a module added to another FEA program, like fe-safe.
What more information do you need regarding question 2? It is possible to re-dissolve precipitates with a solutionizing step, then quench and artificially age to produce new precipitates.
Regarding question 5, here is a nice summary:
You are describing a conversion coating more commonly known as black oxide. Perform an Internet search using those two words and you will find more information.
1. You will liquefy a portion of the part, thereby ruining it for structural purposes.
2. Yes.
3. Not too much, this alloy frequently has large grains and still has high strength.
4. Thermomechanical processing, coupled with alloying (e.g. zirconium), are methods to reduce grain size.
5...
This appears to be a quench crack, which could be due to high concentration of phosphorus, sulfur, or other contaminants.
I am not convinced that normalizing would eliminate this condition, but it may help.
Have a good metallurgical analysis completed (chemical composition, microstructure...
Anodizing is possible, and so it powdercoating. You should preheat the casting (temperature below powdercoating curing point) to de-gas it (entrapped gas porosity is a common condition with high pressure die casting), which will prevent bubbles in the powdercoating.
In my experience, epoxy is the best adhesive for metal to metal joints. 3M Scotch-Weld products are good, and so are a variety of other products from Loctite, Sika, Devcon, etc.
