The spread of integrated structural elements and parts made from low‐density materials (for example aluminum and polymers) created a need for joining technologies with which these can be joined. Herein, the most important surface preparation methods and joining processes, with which the surface structure of aluminum can be modified and aluminum and polymer structures can be joined, are reviewed. For both topics, a new classification method is introduced: surface preparation methods are grouped based on the method of creating surface structures, whereas joining technologies are grouped according to heat input and structural changes in the polymer material. Herein, “hot” joining technologies (in which so much heat is formed that the polymer material is melted) are reviewed. This grouping category includes techniques based on friction and induction, ultrasonic and laser welding, and some in situ joining technologies. With these, materials with highly different chemical structures and melting temperatures are joined in fast cycles, in a reliable manner. In the coming years, more integrated structures containing aluminum–polymer joints manufactured with fast, automatable joining techniques (such as ultrasonic and laser welding, in compliance with the requirements of Industry 4.0) will be used throughout the industry.
The adherability and weldability of pure poly(lactic acid) (PLA) and basalt fibre-reinforced PLA were investigated in this research. The joining efficiency rate is introduced as a comparative parameter among different joining processes. In the case of adhesive bonding, 16 different adhesives were used to join specimens together. The highest bond strength and joining efficiency rate for both the pure (16 MPa, 78%) and basalt fiber-reinforced (18 MPa, 44%) adhesive-bonded specimens was achieved with acrylate-based two-component adhesives. The bond strength and joining efficiency rates of bonded specimens manufactured with four welding technologies (hot gas welding, friction stir welding, ultrasonic welding, laser welding) were also investigated. The highest bond strength for both pure PLA and basalt fibre-reinforced PLA specimens (51 MPa and 125 MPa, respectively) was attained by laser welding. The highest joining efficiency rate for pure PLA specimens (85%) was attained by ultrasonic welding, while it was achieved by laser welding for basalt-fibre reinforced PLA specimens (70%).
In this article, our main aim is to demonstrate and prove that it is feasible to join aluminium and poly(lactic acid) (PLA) specimens by laser beam. We investigated the effects of structuring the surface of the aluminium specimens with corundum blasting and joining speed and used three types of PLA (with the same D-lactide content but different average molecular weights) to investigate the effect of the viscosity of the polymer melt on the load-bearing capacity of the joints. Joined aluminium-PLA specimens were successfully manufactured and examined with standard lap-shear tests. We found that both surface structuring, joining speed and the type of PLA material influenced the load-bearing capacity of the aluminium-PLA joint.
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