Effect of laser surface texturing pattern on mechanical properties in metal-polymer direct joining

• Investigating laser surface texturing (LST)-assisted metal-polymer dissimilar joining. • Joining high-strength steel and polyamide 6 via injection molding. • Obtaining tensile shear strength and fatigue life from mechanical tests. • Verifying the correlation between LST pattern and mechanical properties. In this study, dissimilar materials of galvanized advanced high-strength steel (AHSS) and glass fiber-reinforced polyamide 6 (PA 6) are joined via injection molding to achieve lightweight vehicle structures. To manufacture the AHSS-PA 6 joints, laser surface texturing (LST) is conducted on the AHSS using a nanosecond pulsed laser. Four different LST patterns of vertical, horizontal, orthogonal (a combination of vertical and horizontal), and diagonal (45-degree rotation relative to orthogonal) specimens are created on the AHSS surface with an approximate groove depth of 100 µm. The tensile shear and lateral vibration tests are conducted to mimic mechanical stresses applying on the AHSS-PA 6 joint during road driving. The LST patterns and mechanical stress types strongly influence the mechanical properties of the AHSS-PA 6 joint. The diagonal LST pattern exhibits the largest tensile shear strength (78.2 MPa), whereas the largest fatigue life during the lateral vibration test is attained by the orthogonal LST pattern. For the tensile test, the correlation between the LST pattern and tensile shear test direction is a key factor in determining the tensile shear strength of the AHSS-PA 6 joints, whereas the total length of the AHSS-PA 6 joints governs the fatigue life measured during the lateral vibration test. After the mechanical tests, the fracture surfaces of the AHSS-PA 6 joints are examined to assess the underlying fracture mechanisms.