Try searching for Excel HSC Engineering, Copeland's Student Handbook for Engineering, and An Introduction to Engineering Mechanics by Schlenker.
First two are pretty decent at explaining things, third is awesome for calculation questions, although parts of it are more in depth than what the course covers.
Engineering Materials by Schlenker also has a very detailed (although verbose) explanation of the iron carbon phase diagram, and tells you everything you'd ever need to know for questions relating to the phase diagrams that will be in the HSC course.
Only problem is that both the Schlenker books are out of print as far as I can tell, although you might be lucky and find one in a library or online somewhere.