SANS study of the precipitates microstructural evolution in Al 4032 car engine pistons

Small angle neutron scattering (SANS) technique has been used to study the microstructural evolution of precipitates in real pistons made from commonly used AlSi12CuNiMg alloy. The experiment was performed on new and worn out piston crowns. SANS curves were measured at five different points (possible critical locations) of both pistons. At the central points of the new sample an isotropic scattering was observed, while in the lateral parts of the piston the scattering became anisotropic, indicating the presence of a manufacturing induced texture. The Al-Mg-Si alloys exhibit mechanical properties, which are highly sensitive to thermal treatments. The operating temperature is usually very close or, in certain parts of the crown, can exceed the ageing temperature. A comparison of the ageing treatment-caused alteration of mechanical properties with the changes of the precipitates structure is reported.