Don't have time for a big write up on this but its worth a mention that two hugely monumental hard rock/heavy metal albums were released on 7/25. In 1980, AC/DC released the hugely successful Back in Black, their first record since the death of Bon Scott and first with Brian Johnson on vocals. Although somewhat overplayed, some would argue this is AC/DC's finest album.  

Also, in 1983 Metallica released their debut album Kill Em All. While certainly too heavy for many listeners, this is the album that introduced the world to Metallica and was one of the jumping off points for the thrash movement in the US. Again, some might argue that this was Metallica's finest release. 

Edit: Sorry, got scooped on this as I was putting it together.