Rosenhain established NPL as one of the world's leading research labs in the field of metallurgy
Rosenhain joined NPL in 1906 and during the next 25 years held the position of Superintendent of the Department of Metallurgy and Metallurgical Chemistry, during which time the department grew from only four staff to seventy. He was a brilliant investigator and gained NPL the reputation of being one of the best equipped research laboratories in the world.
From the start it was Rosenhain's aim to undertake fundamental research with every precaution to achieve the highest possible degree of accuracy, and at the same time to meet the growing needs of industry. His book, Introduction to the Study of Physical Metallurgy, was hugely influential.
Prior to the First World War, much of the work in Rosenhain's department was concerned with the ternary alloys of copper, aluminium and manganese, and later with alloys of aluminium and zinc. Several new alloys were developed, the most important being the "Y" alloy containing copper, nickel and magnesium. This alloy proved to have excellent mechanical properties when subjected to the appropriate heat treatment, and it was widely adopted for forgings, particularly when resistance to high temperatures was required.