They had a tremendous fan base so even if they didn't release a new album any particular year, they sold at least one million records from previous album launches. The album Back in Black, is the one that really launched AC/DC into stardom and became the third best selling album of all time (50 million).
The band had its share of tragedy along the way such as in February 1980, a few months after recording the album Highway to Hell, lead singer and co-songwriter Bon Scott died of acute alcohol poisoning. The group considered disbanding but stayed together and brought in another lead singer. While on tour in 2016 their lead singer had to quit the band due to severe hearing loss so Axl Rose (Gun's and Roses), stepped in to finish their tour.
The thing I find most interesting is that the band successfully created an image that would sell albums. I'm sure some parents heard the screaming and maybe some of the lyrics and thought the bandmembers were evil but instead, behind the scenes, they were just normal guys. Very decent guys compared to some rock groups. So congrats to AC/DC for being a member of the Rock and Roll Hall of Fame and also to Angus Young who started the band with his brother Malcolm (who died in 2017). They both performed for over 40 years even when they didn't have to and their fans loved every minute of it.