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The Corrosion Resistance of Aluminum-Magnesium Alloys: Why Do They Survive in the Ocean for So Long?
In today's industry, aluminum-magnesium alloys are widely used in challenging environments such as the ocean due to their excellent corrosion resistance and relatively light weight. The corrosion resistance of these alloys enables them to not only withstand the erosion in the ocean but also remain stable in long-term use. How do aluminum-magnesium alloys survive in these harsh environments? This article will delve into the properties, applications, and corrosion resistance of aluminum-magnesium alloys.
Aluminum-magnesium alloy (AlMg) is mainly composed of aluminum and its main alloying element magnesium. It is a medium-strength, natural alloy with good welding properties.
Composition and characteristics of aluminum-magnesium alloy
Aluminum-magnesium alloys belong to the 5000 series and because they contain up to 5% magnesium, they play an important role in many structural materials. The composition of these alloys makes them difficult to strengthen by heat treatment, and their strength is usually increased by cold working such as coiling and forging. At the same time, the aluminum content of aluminum-magnesium alloy gives it good ductility, while magnesium further improves its corrosion resistance.Aluminum-magnesium alloys are widely used in many fields, including shipbuilding, chemical equipment, pipelines, refrigeration technology and automobiles.
The key to corrosion resistance
The corrosion resistance of aluminum-magnesium alloys depends on many factors, including the chemical composition and structure of the alloy. Studies have shown that the corrosion behavior of aluminum-magnesium alloys is closely related to the solubility of magnesium in α-phase crystals. When the magnesium content is less than 3%, the corrosion resistance of the alloy is usually effectively guaranteed. However, as the magnesium content increases, proper heat treatment becomes critical to ensure that the β phase does not form a continuous film at the grain boundaries. This directly affects the behavior of the alloy in a corrosive environment.If the β phase forms a continuous film, the aluminum-magnesium alloy may experience crevice corrosion in harsh environments, reducing its durability.
Processing and Application
In practical applications, aluminum-magnesium alloys are difficult to process by extrusion because changing the characteristics too much may affect their strength. Common processing methods include rolling, forging, etc., which help maintain the strength of the alloy. Due to their high strength and good welding properties, these alloys are widely used in aerospace engineering. Scandium (Sc) and zirconium (Zr) are often added to further improve welding performance and meet the stringent requirements of aerospace technology.Formation of corrosion-resistant structure
The corrosion resistance of aluminum-magnesium alloys not only depends on their chemical composition, but is also affected by the crystal structure of the alloy. As the temperature decreases, the solubility of magnesium in aluminum gradually becomes far lower than the level at high temperature, which makes the properties of aluminum-magnesium alloy become more stable at lower temperatures. These structural changes significantly improve corrosion resistance after prolonged heat treatment.After proper heat treatment, the grain boundaries in the alloy will transform and eventually form a uniform particle structure, thereby improving corrosion resistance.
