Influence of Ni-Cu-Fe surface nanocomposite reinforcement on the corrosion resistance of AA1050 aluminum alloy for ocean thermal energy conversion heat exchangers

In the current study, friction stir alloying (FSA) was carried out to alter the surface microstructure of AA1050 aluminum alloy using (Ni-Cu-Fe) nano additives metal powder (NAMP) with different mixtures . Microstructural changes and corrosion characteristics were determined before and after the FSA process. During this experiment, potentiodynamic polarization analysis and electrochemical impedance spectroscopy (EIS) were conducted in a 3.5 wt% NaCl electrolyte. The base alloy 1050 without nano-reinforcement exhibited a flawless microstructure but was less effective compared to the reinforced samples due to the absence of reinforcing phases. In contrast, the alloy reinforced with 20Ni-40Cu-40Fe additives demonstrated the best microstructure among all samples. This alloy exhibited a highly homogeneous structure with fine properties and a well-distributed reinforcing phase, indicating ideal processing conditions. When the weight percentage of nickel increased and the percentages of both copper and iron decreased in the surface reinforcement of the alloy, defects, signs of reduced homogeneity, agglomeration, and discontinuity in the microstructure began to appear. The images showed the worst microstructure in the 100% nickel-reinforced alloy, where severe agglomeration, irregular distribution, and increased surface defects were prevalent. All electrochemical analysis results showed excellent agreement. The base alloy without additives exhibited poor corrosion resistance with a corrosion current density ( I corr. ) of 2.2709E-05 A, while the additive-enhanced samples showed high corrosion resistance with I corr of approximately 1.6418×10 -5 , 1.5864×10 -5 , and 1.3137×10 -5 A for the samples (60 Ni-20 Cu-20 Fe), (40 Ni-30 Cu-30 Fe), and (20 Ni-40 Cu-40 Fe), respectively.