Aluminum alloys play a critical role in hydrogen storage and transportation due to their unique combination of lightweight properties, corrosion resistance, and structural integrity. These alloys are particularly advantageous in applications such as cryogenic tanks for liquid hydrogen, high-pressure gas storage, and transport vessels. Their ability to withstand harsh environments while maintaining mechanical performance makes them a preferred material in hydrogen infrastructure.

One of the most significant advantages of aluminum alloys is their low density, which contributes to weight reduction in storage and transport systems. This is especially important for mobile applications, such as hydrogen fuel cell vehicles and aerospace systems, where minimizing weight directly impacts efficiency and operational costs. Compared to steel, aluminum alloys offer a weight reduction of up to 65%, making them ideal for applications where mass is a critical factor.

Corrosion resistance is another key attribute of aluminum alloys in hydrogen environments. Aluminum naturally forms a thin oxide layer when exposed to air, which provides inherent protection against corrosion. This passive layer is stable in both aqueous and gaseous hydrogen environments, reducing the risk of material degradation over time. However, in certain conditions, such as exposure to high-pressure hydrogen or cryogenic temperatures, additional treatments like anodization are employed to enhance corrosion resistance. Anodization thickens the oxide layer, improving durability and wear resistance while maintaining the alloy's lightweight properties.

Several aluminum alloy series are commonly used in hydrogen applications, with the 5000 and 6000 series being the most prevalent. The 5000 series, particularly alloys like 5083 and 5456, are known for their excellent corrosion resistance and high strength, making them suitable for cryogenic storage tanks and marine environments. These alloys are primarily composed of aluminum-magnesium, which enhances their mechanical properties without compromising weldability.

The 6000 series, including alloys such as 6061 and 6082, are widely used in structural components due to their balance of strength, formability, and weldability. These alloys are aluminum-magnesium-silicon based, offering good corrosion resistance and moderate strength, making them ideal for hydrogen transport vessels and piping systems. While not as strong as the 5000 series at cryogenic temperatures, the 6000 series alloys are often chosen for applications where a combination of fabrication ease and performance is required.

Weldability is a critical factor in the fabrication of hydrogen storage and transport systems. Aluminum alloys generally exhibit good weldability, but certain precautions must be taken to avoid defects such as porosity or cracking. The 5000 series alloys are particularly well-suited for welding due to their magnesium content, which helps stabilize the weld pool and reduce hot cracking. The 6000 series alloys require more careful control of welding parameters, as they are prone to softening in the heat-affected zone. Techniques such as friction stir welding and laser welding are often employed to maintain joint integrity and minimize distortion.

In cryogenic hydrogen storage, aluminum alloys are favored for their ability to maintain ductility at extremely low temperatures. Liquid hydrogen is stored at around -253°C, a condition under which many materials become brittle. Aluminum alloys, however, retain their toughness and fracture resistance, making them reliable for cryogenic tanks. Alloys like 5083 are commonly used in these applications due to their proven performance in liquefied natural gas (LNG) storage, which operates at similarly low temperatures.

High-pressure hydrogen storage also benefits from aluminum alloys, particularly in composite overwrapped pressure vessels (COPVs). These vessels consist of an aluminum liner wrapped with carbon fiber, combining the liner's hydrogen compatibility with the fiber's high strength-to-weight ratio. The aluminum liner provides a hermetic seal while preventing hydrogen permeation, a common issue with polymer-based liners.

Despite their advantages, aluminum alloys are not without challenges in hydrogen applications. Hydrogen embrittlement, though less severe than in high-strength steels, can still occur under certain conditions. Prolonged exposure to high-pressure hydrogen may lead to reduced ductility and crack propagation in some aluminum alloys. Research indicates that alloys with fine-grained microstructures and controlled impurity levels exhibit better resistance to hydrogen-induced degradation.

Another consideration is thermal expansion. Aluminum has a higher coefficient of thermal expansion compared to steel, which must be accounted for in system design to avoid stress buildup during temperature fluctuations. This is particularly relevant in cryogenic systems where large temperature differentials are common.

The use of aluminum alloys in hydrogen infrastructure is supported by extensive industrial experience and standardization. Organizations such as the American Society of Mechanical Engineers (ASME) and the International Organization for Standardization (ISO) provide guidelines for the safe use of aluminum in hydrogen service. These standards cover material selection, fabrication practices, and inspection protocols to ensure reliability and safety.

Looking ahead, advancements in aluminum alloy development continue to enhance their suitability for hydrogen applications. Research is focused on improving strength-to-weight ratios, corrosion resistance, and hydrogen compatibility through microstructural engineering and alloying innovations. Additive manufacturing techniques are also being explored to produce complex aluminum components with optimized properties for hydrogen storage and transport.

In summary, aluminum alloys are indispensable in hydrogen storage and transportation systems due to their lightweight nature, corrosion resistance, and performance under cryogenic conditions. The 5000 and 6000 series alloys dominate these applications, offering a balance of strength, weldability, and durability. While challenges such as hydrogen embrittlement and thermal expansion exist, ongoing research and industrial best practices ensure that aluminum remains a cornerstone material in the growing hydrogen economy.