What material makes a lousy lock?

This door lock is broken. Succumbed to repeated pulling. But by right, door lock should be able to withstand vigorous pull and push and even twist.

Why this door lock failed?

The failure is caused by its material. It is made of Zinc Diecast. Which is a bad choice for door lock. Zinc is a not-so-strong material. Die casted (and mixed with some other cheaper material) makes it even weaker. Just take any Zinc Diecast. Bend it, and bend it back to original (just once), it will break. 
What is the minimum material you should go for a lock? Zinc Alloy. Not really strong, but so much better than diecasted. But remember, it is a minimum. Go for a better one if you can afford. Not to show off, not to luxury, but for your family’s safety, and for saving yourself some trouble.

Advise from Locksmith, not Salesman.

www.finelockshop.com