How does squeeze casting improve the mechanical properties and fatigue life of electric bicycle connection assemblies?
Publish Time: 2026-01-22
With the trend towards lightweight, high-rigidity, and long-life electric bicycles, key structural components—especially frame connection assemblies—face higher demands on material properties and manufacturing processes. While traditional die casting is low-cost and efficient, internal defects such as porosity and shrinkage severely limit its strength and durability; while forgings, although possessing excellent performance, are difficult to form complex structures and are costly. Squeeze casting, as a near-net-shape forming technology between die casting and forging, is becoming an ideal solution for improving the mechanical properties and fatigue life of electric bicycle connection assemblies.1. Dense Structure: Eliminating Performance "Shortcomings" at the SourceThe core advantage of squeeze casting lies in its high-pressure feeding mechanism. After the molten metal is filled into the mold, the mold is closed and a continuous pressure of tens to hundreds of megapascals is applied, causing the solidification process to occur under high pressure. This process effectively suppresses porosity and shrinkage caused by gas entrapment and solidification shrinkage in traditional die casting, significantly improving the density of the casting to near the level of forgings. For connecting components subjected to alternating loads, internal defects are often the initiation source of fatigue cracks. Extrusion casting significantly delays crack propagation by eliminating these microscopic "weak points," thereby significantly improving fatigue life—experiments show that the fatigue strength of extruded castings can be more than 30% higher than that of ordinary die-castings of the same material.2. Fine-grained strengthening: Optimizing microstructure to improve overall performanceHigh pressure not only compacts the metal but also promotes nucleation and inhibits grain growth, forming a fine and uniform equiaxed grain structure. Simultaneously, some processes combine semi-solid slurry or localized chilling techniques to further refine the dendrite spacing. Fine-grained structure brings dual benefits: on the one hand, according to the Hall-Page relation, the finer the grains, the higher the yield strength and hardness of the material; on the other hand, a fine-grained structure can more evenly distribute stress, reducing localized stress concentration and improving impact and deformation resistance. This is crucial for connecting components in electric bicycles operating under frequent starts, stops, and sudden braking on bumpy roads, ensuring they do not fail under long-term dynamic loads.3. Material Compatibility: Efficient Forming of High-Strength Aluminum AlloysElectric bicycle connection assemblies commonly utilize A356, ADC12, or novel Al-Si-Mg series high-strength aluminum alloys. These materials exhibit excellent fluidity and hot-cracking resistance under extrusion casting conditions. Furthermore, subsequent T6 heat treatment can further precipitate strengthening phases, achieving a synergistic improvement in strength and toughness. The slow filling and high-pressure solidification characteristics of extrusion casting effectively avoid problems such as cold shuts and incomplete filling in thin-walled complex structures, allowing designers to boldly adopt integrated, topology-optimized lightweight structures—for example, integrating multiple mounting holes, reinforcing ribs, and curved surface transitions into a single unit, reducing weight while improving overall rigidity.4. Dimensional Accuracy and Surface Quality: Reduced Post-Processing, Ensuring Assembly ReliabilityThe dimensional tolerances of extruded castings are far superior to those of sand castings, approaching the level of die casting. This means that critical mating surfaces of connection components can directly meet assembly requirements, significantly reducing machining and avoiding the introduction of new defects due to damage to the dense surface layer caused by cutting. Simultaneously, high surface integrity reduces stress concentration sources, further extending fatigue life.
Electric bicycle connection assemblies offer near-forged mechanical properties and reliability far exceeding die-casting, while also balancing complex structures with mass production economics. In today's pursuit of safe, durable, and green transportation, this process is not only a choice for manufacturing upgrades but also a key support for leaping product quality.
