The Germans had various shortages of critical alloys, but few that would effect aircraft production. Wood was sometimes used for propellers since the war's beginning, because it had some advantages over metal props, it was entirely out of choice. Wooden compontents were used not because of aluminium shortage (Germany was the 2nd largest producer after the US) but because it allowed the use of skilled woodworking shops for the aircraft industry. Copper was in short supply as was chromium (Turkey) and nickel (Finland) but it was not critical until the wars end; OTOH face hardened armor was simply dropped because it was not practical for the increased armor thicknesses, which called for more softer and more ductile armor that resisted rounds better, and techniques such as sloped armor (besides face hardening being time consuming and more of a question of capacity, rather than alloy). Some alloys were dropped from armored steel but were substituted by others (rather expensive, but available vanadion was used instead of molybdenium, but vanadium is also a very effective alloy). Most alloys in steel industry are replacable by others.
In the end, weapon production was never critical, though hurt by Allied bombing, the Germans always had plenty of guns. Their critical bottlenecks were fuel (which was hurt by the SBC as much as by the Red Army's advance, the latter also effected some critical alloy supplies in Ukraine) and manpower.
