Just aluminium cyanide, no Roman numeral is needed here.
Aluminium is a special case because you'll sometimes see it listed as a metalloid, but more often than not it is characterized as metal.
SImply put, aluminium will always have a
In your case, break up the compound into cation and anion. The subscripts of the cation becomes the charge of the anion, and vice versa - this is known as the criss-cross rule.
#"Al"_color(blue)(1)("CN")_color(red)(3) -> "Al"^color(red)(3+) + 3"CN"^color(blue)(1-)#
The only rule you need to follow is the use of the suffix -ide for the anion, which in this case is the cyanide anion,
The name of the compound will thus be aluminium cyanide,