Laser Processing of Aluminum Alloys: Hypereutectic Al-Si Surface Remelting and Al6061- RAM2 Additive Manufacturing

Abstract

This dissertation undertakes a comprehensive exploration of laser processing of Aluminum alloys. The studies began with laser surface remelting, which is a basic form of laser-matter interaction. In Chapter 3, Aluminum-Silicon surface remelting experiments were designed around the laser, utilizing its ability to induce many different heat histories within the interaction zone. Microstructure transformation (from flakes to the fibers), microstructure refinement (increasing more than 100 times), creation of fully eutectic area (up to 90% of the processed area), and extension of the solid solubility limit of Aluminum due to high cooling rates were reported in this chapter. A processing-structure relationship was presented in terms of the undercooling amount (ΔTk) for the readers’ understanding. Additionally, the nano-mechanical hardness measurements of the laser-processed region were reported, and it was discovered that the laser-affected area was 1.5 times harder than the base plate. After a certain knowledge of laser surface remelting, the research advances to additive manufacturing of commercial-grade Aluminum alloys: Al7075 (consisting of ~ 6% Zinc, 2.5 % Magnesium, 1.5 % Copper, and 1% Silicon) and Al6061-RAM2 (comprising of ~0.9% Magnesium, 0.7% Silicon, 0.6% Iron) reactive additive manufacturing variant with 2% ceramic addition. The former one studied for increasing the process yield by online defect detection, while the latter was for scaled-up prototyping. In Chapter 4, plasma signals emanating from laser-material interaction were monitored for defects (voids and cracks) detection within seconds. These signals are compared with the μCT data to identify and locate the defects. It was demonstrated that a randomly chosen spectrum signal can reveal a defect with 87% accuracy. Chapter 5 investigates the direct metal deposition of Al6061-RAM2 in search of a printing strategy capable of creating functional prototypes at 1:100 and 1:20 scales. Preliminary studies within this chapter affirmed the ability to produce a rectangular coupon with less than 2.5% porosity. Scaled prototypes at 1:20 for wind blade manufacturing molds (dimensions of 50x50x15 cm) were generated, showcasing intricate interior details due to topology optimization, based on the previous chapter’s findings. These printed modules underwent testing for dimensional accuracy and vacuum integrity, to confirm the absence of connected porosities from production states. The results were highly satisfactory, asserting the practicality of direct metal deposition for creating complex molds at a 1:1 scale.