Is aluminium stronger than steel?
Nope, to check this answer, do an experiment: hammer a piece of
aluminum foil. You will see that it creases easily wheres steel
cannot be broken down easily.
However, aluminum is also more light-weight than steel. Aluminum
is cheaper to manufacture, easier to bend as needed into a variety
of shapes, can be shipped more easily (less weight=less cost), and
makes many items lighter in weight (cars, airplanes, etc.)
The one big drawback is that cars used to have steel bumpers.
Since most are now steel or plastic, and bumpers are often the
first to make contact with another car or object, the bumper is
less sturdy now than when it was steel.