The standard material for an Xpandrel is 6061 Aluminum.
Each series has different specific material needs based on the design. Materials can sometimes be readily substituted other times some design work may need to be done to accommodate the forced & deflection of the new material properties.
Harder materials such as 7075, 4041, & D2 are generally reserved for small diameters, long length to diameter ratios and the 2000 series models.
5000 Series always uses a 6061 body with various steel alloy internal components and 4140-
Material Designations in Part Numbers:
* harder materials may affect the expansion . Designs may be modified to accomdate that however, aluminum is the prefered body material