for purchasing aluminium are the grades to be mentionedAluminum alloy designations are described by a 4-digit index system. The first digit indicates the alloy group according to the major alloying elements. 1XXX - 99% Al with no major alloying element. 2XXX – copper 3XXX – Manganese 4XXX – Silicon 5XXX – Magnesium and silicon 7XXX – Zinc 8XXX – other element Experimental alloy designations have an “X” prefix Aluminum temper designations (suffixes) describe heat-treatable and non heat-treatable alloys.If it is a product for work, yes engineers and purchasers specify the grades. If for hobby then it is up to you. Common extruded shapes (beams, tubes, angles) - 6061-T6 - 6063-T5 -T6 specifies tempering class. Actually both alloys come in various T4, T5, etc., the above are just two common combinations. 6061 is a little stronger, and T6 gets its strength up quite good. Beware that welded joints are weaker since heat removes the strength from tempering. Some common sheets - 6061 (strength) - 5052 (strength, welds better than 6xxx, good formability) - 5068 (some call it \'marine grade\' for corrosion resistance) Sheets can come in many alloys.... you may get cheaper grades if you don\'t need one of these. (if you are casting - there\'s whole other system of grades.) The above are just common grades. For high strength requirement you may need a specific grade in the 7xxx family.Other related question