Why is the aluminum in a tin can harder than aluminum can? What characterizes their different properties?
Aluminum vs. Tin
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. It is a silvery-white, soft, non-magnetic and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; it is the third most abundant element after oxygen and silicon and the most abundant metal in the crust, though it is less common in the mantle below.
Tin is a chemical element with the symbol Sn (from Latin: stannum) and atomic number 50. Tin is a silvery metal that characteristicly has a faint yellow hue. Tin, like indium, is soft enough to be cut without much force. When a bar of tin is bent the so-called "tin cry" can be heard as a result of sliding tin crystals reforming; this trait is shared by indium, cadmium and frozen mercury. Pure tin after solidifying keeps a mirror-like appearance similar to most metals. However, in most tin alloys (such as pewter) the metal solidifies with a dull gray color. Tin is a post-transition metal in group 14 of the periodic table of elements. It is obtained chiefly from the mineral cassiterite, which contains stannic oxide, SnO2.
With that out of the way. It seems that Tin cans are made of Steel while Aluminum cans are made of Aluminum.
Tin Can vs Aluminum Can
A tin can, tin (especially in British English, Australian English and Canadian English), steel can, steel packaging or a can, is a container for the distribution or storage of goods, composed of thin metal. Many cans require opening by cutting the "end" open; others have removable covers. Cans hold diverse contents: foods, beverages, oil, chemicals, etc. Steel cans are made of tinplate (tin-coated steel) or of tin-free steel. In some dialects, even aluminium cans are called "tin cans".
Aluminum beverage can with stay-tab easy-opening. Note the can is narrowed at the top to allow for a smaller “end” An aluminum can (British English: aluminium can), sometimes erroneously referred to as a "tin can", is a container for packaging made primarily of aluminum. It is commonly used for foods and beverages such as milk and soup but also for products such as oil, chemicals, and other liquids. Global production is 180 billion annually and constitutes the largest single use of aluminum globally.
Wikipedia has an extensive discussion of containers and packaging.
The Moh's scale seems to place Aluminum at a 3 and Steel at a 4. This might be a chemistry question rather than a physics question.
A separate check suggests that tin is quite soft.