We have implemented alloys and metal related information at one of the largest aluminium manufacturer using AX before. You need to have a separate product for each measurement you have that you refer as dimension and each type of metal including all variations. To set the values as separate fields, you would use the product category hierarchy (i.e. we used it for distinguishing between parts and various finished product types), and product attributes (type of alloy, cut length/width, special treatments, etc). You can have as many product attributes created as you want, you can default the values by product category type, it is a very flexible setup.
For the products to be easily searchable we have also done a customization, where if the product attributes were added/changed, we have automatically generated a search name out of the fields which we have set up a sequence for to be included in the product name, and set the search name on the released product based on those attributes.
I do not know about NAV, try asking it on the forum dedicated for that.