the bottom line is the 150 AL-31s from Russia are for old version J-10s and J-11 as spare parts... as AL-31's lifespam is less than 900 hours which is far less than a plane's service length, therefore every one plane needs at least 2-3 engines for its entire service length (western standard)..but in Russian's standard the requirement will go well up to 4-6 engines per plane.
Chinese TH WS-10 acheived lifespam of 1600 hours after a decade of non-stop rigorous ground tests, it is inevitable going to replace AL-31 and any other russian engines, thats why we see newer versions planes like J-11B and J-15, J-10B and J-20 are all using TH engines to power them, the russian engine is phased out for PLAAF's new planes.
however some clowns here sticking their inferior complexity mentality on the issue of China buys 150 engines from Russia to make fun of China's turbofan industry whereas neglecting the fact that there is a self-proclaimed 'technology powerhouse' cannt even produce reliable 1950s standard turbojet engine and glorified by the record holding 1000 real-time crashing world record..isnt it too funny ?
