Will I get a warranty for my mobile if I purchase from Aliexpress?

Depends on the supplier. Make sure to verify this with the seller at Aliexpress. Of course there is legislation about this. For example all electronic products in Europe have a one year guarantee. Still you will need to sue the company of they don't give it to you. When you buy at Aliexpress just make sure to selected sellers that are already on the platform for some time or offer after sales support.