Why is aluminium alloy stronger than pure aluminium?

Well I'm not a metallurgist,but here goes eg; Zinc is a soft natural metal as is copper,but when they are mixed we have brass, whicch is harder but more brittle,or you can have iron ore, on its own will break verry easily but if you add 2 percent mg it becomes workable and stronger.

Another method of making a piece of metal stronger eg;samuari sWord,where you have temperd steel with a harder alloy for cutting edge and would take 3 months to make,i think

an alloy is stronger than pure metal because in a pure metal all the atoms are the same size and ordered. but when another element is added it shifts the atoms making the layers harder to shift, therefore making it stronger.