Interfacial corrosion behavior of AA2195/TC4 composites prepared by friction stir additive manufacturing

Aluminum-titanium composite materials are widely used in the aerospace field due to their high specific strength and excellent corrosion resistance. Al-Cu-Li alloys, known for their high specific strength and stiffness, are considered an ideal choice for preparing lightweight and high-strength aluminum-titanium composites. However, the relatively low melting point, low density, and high thermal conductivity of Al-Cu-Li alloys lead to significant differences in physical and chemical properties between Al-Cu-Li alloys and Ti alloys. Therefore, the processability of Al-Cu-Li and TC4 alloys via friction stir additive manufacturing (FSAM) is more challenging compared to conventional Al alloys. In this work, the lightweight and high-strength AA2195 aluminum alloy and TC4 titanium alloy for aerospace were selected. The AA2195/TC4 composites were prepared by FSAM. Combined with DFT calculation, the corrosion mechanism of the AA2195/TC4 joint interfaces was deeply revealed. The corrosion resistance and corrosion behavior of the joint interfaces of AA2195/TC4 composites prepared by FSAM in 3.5 wt.% NaCl solution were investigated through electrochemical tests and quasi-in-situ immersion corrosion tests. The results show that the corrosion current density of the prepared AA2195/TC4 composites is 1.49×10 -8 A/cm 2 , and it has electrochemical corrosion resistance between AA2195 aluminum alloy (1.20×10 -7 A/cm 2 ) and TC4 titanium alloy (9.37×10 -9 A/cm 2 ). During the corrosion process, initially only slight pitting occurred on one side of AA2195 aluminum alloy. As corrosion duration increased, the alloy near the interfaces transitioned from pitting to severe intergranular corrosion. Meanwhile, the Scanning Kelvin probe force microscopy (SKPFM) results show that the AA2195 aluminum alloy near the joint interfaces has the largest surface potential difference with Al-Ti intermetallic compounds (IMCs), with a value of 142.98 mV, and thus the corrosion phenomenon is the most severe. Furthermore, the surface work functions of Al(111), Ti(001), TiAl 2 (001), and TiAl 3 (100) were calculated respectively through density functional theory (DFT) calculations. The results show that Al(111) has the smallest surface work function, explaining its propensity for preferential corrosion. This work fundamentally reveals the corrosion mechanism of the Al/Ti composites joint interfaces prepared by FSAM and provides a scientific basis for the preparation of AA2195/TC4 composites for aerospace.