JAC270D is a low carbon cold-rolled steel suitable for deep drawing. Ultimate tensile strength > 270 MPa, yield strength (depends on thickness, this is for 1 mm < t < 3.2 mm) 115-205 MPa. The composition is not explicitly defined, but it must be sufficiently resistant to aging (no stretcher strains for at least 3 months manufacturing). I am not familiar with the designation X621 for an aluminum alloy. Is this a casting or sheet metal?

For the aluminium alloy, the only thing close that comes to mind is the Alcoa alloy X6022 and 6111. The X has been dropped. Here is some information:

http://www.alcoa.com/mill_products/catalog/pdf/All...

Both the X621 aluminum and the JAC270D steel are in sheet form. I am dealing with 1 mm thick sheet metal for both the aluminum and the steel. We are trying to run some thermal load tests on them.