Whilst working in military research centre in Neubabelsberg in 1901, Wilm discovered age hardening, in particular age hardening of aluminium alloys. This discovery was made after hardness measurements on Al-Cu alloy specimens were serendipitously found to increase in hardness at room temperature. This increase in hardness was identified after his measurements were interrupted by a weekend, and when resumed on the Monday the hardness had increased.
By 1906, Wilm had developed an alloy – Al-3.5–5.5%Cu-Mg-Mn, Mg and Mn were < 1%, for which a patent was filed. Later this patent was purchased and the alloy marketed as duralinium. Somewhat unusually Wilm did not write his first article on age hardening until 1911. At the time Wilm was developing an aluminium alloy to replace brass in ammunition. He left research and later became a farmer in 1919, until his death.