Size dependency of mechanical properties of high purity aluminium foils

In order to study the size effect, tensile tests with high purity aluminium foils of different thicknesses from 5 μm to 540 μm were performed at room temperature and at 100 deg. C. A pronounced size effect was observed especially at elevated temperature. There are two major contributions to the size effect: first, the samples get weak if the fraction t/g of thickness t to grain size g is smaller than 1, because the Hall-Petch model can no longer be applied if most of the grain boundaries are at the free surface. Second, the presence of an oxide layer increases the tensile strength of thin foils. Our results are relevant for the prediction of reliability and life time of electronic devices. It may be concluded that the grain size should be refined when the dimensions of electronic parts are reduced.