Microstructure, mechanical, and corrosion properties of Al–10Si and Al–10Si–2Cu alloys with different La contents

The effects of La content on the microstructure, mechanical properties, and corrosion behavior of Al–10Si and Al–10Si–2Cu alloys were studied. With the addition of a certain amount of La to these alloys, the grain refinement effects of α-Al were confirmed to be 16.4% and 18.6%, respectively. In addition, precipitates of the Al–Si–La and Si–Cu–La phases were formed in the form of a core-shell structure with the addition of La. Owing to the grain refinement and precipitation strengthening effects, the hardness was improved by 5% and 10.9%, respectively. The Al–10Si–2Cu alloy was found to have better mechanical properties than the Al–10Si alloy because the dispersibility of Cu-related precipitation phases could be improved by the attraction with La during Cu precipitation. The addition of La also improved the corrosion resistance. Both Al–Si and Al–Si–Cu alloys showed improved corrosion resistance owing to the grain refinement effect, and the improved effect was greater in Al–Si–Cu alloys. This is because the growth of Al2Cu, which is the main cause of galvanic corrosion, was suppressed, attributed to the formation of a Si–Cu–La phase by the addition of La instead of Al2Cu. The potential analysis showed that the potential difference between the newly formed Si–Cu–La phase and the α-Al phase was found to be 21% lower than the potential difference between the α-Al and Al2Cu phases. These results confirmed that the corrosion resistance improvement effect of the Al–Si–Cu alloy was greater than that of the Al–Si alloy with the addition of La.