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High-performance wrought aluminum alloys, particularly AA6061, are pivotal in industries like automotive and aerospace due to their exceptional strength and good response to heat treatments. Investment casting offers precision manufacturing for these alloys, because casting AA6061 poses challenges like hot cracking and severe shrinkage during solidification. This study aims to address these issues, enabling crack-free investment casting of AA6061, thereby unlocking the full potential of investment casting for high-performance aluminum alloy components.

Nanotechnology is used to enhance the investment casting process, incorporating a small volume fraction of nanoparticles into the alloy melt. The focus is on widely used aluminum alloy 6061, utilizing rapid investment casting (RIC) for both pure AA6061 and nanotechnology-enhanced AA6061. Microstructural characterization involved X-ray diffraction, optical microscopy, scanning electron microscopy, differential scanning calorimetry and energy dispersive X-ray spectroscopy. Mechanical properties were evaluated through microhardness and tensile testing.

The study reveals the success of nanotechnology-enabled investment casting in traditionally challenging wrought aluminum alloys like AA6061. Achieving crack-free casting, enhanced grain morphology and superior mechanical properties, because the nanoparticles control grain sizes and phase growth, overcoming traditional challenges associated with low cooling rates. This breakthrough underscores nanotechnology's transformative impact on the mechanical integrity and casting quality of high-performance aluminum alloys.

This research contributes originality and value by successfully addressing the struggles in investment casting AA6061. The novel nano-treating approach overcomes solidification defects, showcasing the potential of integrating nanotechnology into rapid investment casting. By mitigating challenges in casting high-performance aluminum alloys, this study paves the way for advancements in manufacturing crack-free, high-quality aluminum alloy components, emphasizing nanotechnology's transformative role in precision casting.

Additive manufacturing (AM) can achieve significant weight savings with only minor compromises in strength if high-performance wrought aluminum alloys are used as feedstock. Despite the advantages in strength that aluminum alloys (AA) 6061 offer, they cannot be manufactured via printing because of hot cracking and other solidification problems. The purpose of this study is to achieve high-quality printing of AA6061 with nanotreated wires.

Nanotreating was used to modify the AA6061 alloy composition by adding a small fraction of nanoparticles to enhance the alloy’s manufacturability and resultant properties. Wire arc additive manufacturing (WAAM) was used to print the nanotreated AA6061 wire feedstock. The microstructure of the printed AA6061 was characterized by X-ray crystallography, optical microscopy, scanning electron microscopy and energy dispersive spectroscopy mapping. The microhardness profile, tensile behavior and fracture surface were analyzed.

This work successfully used WAAM to print nanotreated AA 6061 components. The resulting AA6061 parts were crack-free, with exceptional grain morphology and superior mechanical properties. Owing to the excellent size control capabilities of nanoparticles, a homogeneous distribution of small grains was maintained in all deposited layers, even during repeated thermal cycles.

Previous studies have not successfully printed AA6061 using WAAM. Conventional WAAM products exhibit anisotropic mechanical properties. The nanotreated AA6061 was successfully printed to achieve homogeneous microhardness and isotropic tensile properties. The promising results of this study reflect the great potential of nanotech metallurgy as applied to the WAAM process.

The cities, for the most part, appeared up until the middle of the 1990s to be islands within the larger Chinese political economy in which job-secure workers could be certain that their livelihood, health, education, and living abodes would evermore undergird their and their children's sustenance. At least until the late 1980s, urbanites who stuck with the state sector even considered good treatment on the job a kind of birthright, an entitlement that was sure to be enforced. In the cities, true, there had always been the disadvantaged after 1949 – those without offspring or spouses, the disabled, and people unable to support themselves. But this relatively tiny batch of individuals generally survived in the shadows and out of sight, subsisting – but just barely – as members of the “three withouts” on a mere pittance, in the form of meager “social relief” disbursed by civil affairs departments.⁸