<p>High-pressure die casting is extensively employed in the automotive sector for producing lightweight aluminium components. However, porosity remains a critical casting defect that compromises structural integrity and mechanical performance. This study explores the effectiveness of integrating steel inserts in aluminium HPDC swing arms to mitigate porosity and improve mechanical strength. Comparative assessments between conventional and steel-insert-reinforced swing arm designs were conducted using X-ray radiography and computed tomography to quantitatively analyze porosity distribution. Experimental results revealed a substantial porosity reduction of 76.92% at critical regions due to insert integration. The mechanical reliability of the components was further validated through thread stripping strength analysis and high-speed durability testing. The redesigned swing arm exhibited enhanced load-bearing capacity and extended service life by 63.63%, outperforming the conventional design. The findings confirm that steel inserts function as localized thermal sinks, promoting controlled solidification and minimizing shrinkage-induced porosity in high-stress regions. This work establishes steel insert integration as a viable strategy for enhancing the performance, fatigue resistance, and durability of aluminium HPDC components in automotive applications. Future work will explore alternative insert materials and process refinements to further improve casting quality.</p>