Imagine a material as light as a feather yet strong as steel—such a breakthrough would transform industries. Magnesium alloys offer this remarkable potential, but they face a critical challenge: when their strength increases, their toughness decreases, limiting their ability to replace traditional metals. Is there a way to make magnesium alloys both strong and tough? The answer lies in shot peening technology.

In an era prioritizing energy efficiency and environmental sustainability, lightweight design has become essential. Magnesium alloys stand out among metals for their exceptional strength-to-weight ratio, making them ideal for reducing weight without sacrificing performance. In automotive applications, magnesium components can decrease vehicle weight, improving fuel efficiency and reducing emissions. In aerospace, lighter aircraft structures enhance flight performance and lower operational costs.

Despite their advantages, magnesium alloys face limitations. A key issue is balancing strength and toughness—a "seesaw effect" where improving one often weakens the other. Magnesium's crystalline structure and limited slip systems at room temperature result in poor plastic deformation resistance, increasing the risk of brittle fracture. This poses safety concerns in high-stress applications.

When overall material properties prove difficult to optimize, surface modification offers an alternative. Research shows that most material failures originate at the surface. By reinforcing the surface—enhancing wear resistance, fatigue strength, and other properties—engineers can significantly extend a material's lifespan and reliability. Think of it as a protective "armor" shielding the material from external damage.

Recent advances in gradient microstructure design provide a promising solution. This approach creates a gradual transition in grain size and structure from the surface to the core, combining surface hardness with interior toughness. Picture a cake with a crisp caramel layer outside and soft cream inside—the gradient microstructure similarly balances strength and flexibility.

To create this gradient structure in magnesium alloys, shot peening technology proves invaluable. This cost-effective surface treatment bombards the material with high-speed micro-projectiles (typically steel or ceramic beads), inducing plastic deformation that alters surface microstructure and mechanical properties. Imagine countless tiny hammers compacting the surface, making it denser and harder.

Shot peening enhances material performance through three primary effects:

1. Plastic Deformation: The impact of projectiles causes surface hardening, significantly increasing strength and hardness—like adding a protective shell.

2. Lattice Defects: The process generates dislocations and vacancies that impede further deformation, boosting strength—similar to creating internal obstacles.

3. Grain Refinement: Intense deformation breaks down surface grains, even forming nanocrystals. Smaller grains mean more boundaries, further resisting deformation—akin to turning boulders into gravel.

While conventional shot peening mainly improves fatigue resistance, "Severe Shot Peening" (SSP) uses higher-intensity parameters to create deeper, more pronounced gradient structures—like a deep-tissue massage for metals.

AZ31, a widely used magnesium alloy with excellent formability and weldability, shows particular promise for replacing aluminum and steel in vehicles. However, its strength-toughness balance requires improvement. Twin-Roll Casting (TRC), an innovative production method, offers finer grain structures at lower costs compared to traditional rolling.

Researchers tested TRC-produced AZ31 sheets with varying shot sizes (0.40–3.18mm) and air pressures (0.06–0.22MPa), analyzing microstructure and mechanical properties. Key findings:

• Larger shots create deeper deformation layers but may increase surface roughness.

• Higher pressures intensify impacts but risk surface cracking.

• Longer peening boosts hardness but may cause fatigue damage.

Post-peening annealing at 150°C further improved ductility without sacrificing strength.

Shot peening opens new possibilities for magnesium alloys. By precisely controlling parameters, engineers can tailor gradient structures to optimize multiple properties simultaneously. As this technology evolves, magnesium alloys will find broader use in automotive, aerospace, and electronics—advancing lightweight, sustainable engineering solutions.