Metal–polymer hybrid structures are becoming desirable due to their wide range of applications in the automotive, aerospace, biomedical and construction industries. Properties such as a light weight, high specific strength, and design flexibility along with the low manufacturing costs of metal–polymer hybrid structures make them widely attractive in several applications. One of the main challenges that hinders the widespread utilization of metal–polymer hybrid structures is the challenging dissimilar joining of metals to polymers. Friction stir welding (FSW) shows a promising potential in overcoming most of the issues and limitations faced in the conventional joining methods of such structures. Several works in the literature have explored the FSW of different metal-to-polymer combinations. In some of the works, the joints are examined based on processing parameter optimization, microstructural characteristics, and mechanical performances. It is, therefore, important to summarize the findings of these works as a means of providing a reference to researchers to facilitate further research on the utilization of FSW in joining metals to polymers. Thus, this work aims to present a comprehensive technical review on the FSW technique for joining metals to polymers by reviewing the reported literature findings on the impact of materials, tools, process parameters, and defects on the strength and microstructure of the produced joints. In addition, this work reviews and presents the latest practices aiming to enhance the metal–polymer joint quality that have been reported in the literature.

Transitioning to zero-emission vehicles (ZEVs) is thought to substantially curb emissions, promoting sustainable development. However, the extent of the problem extends beyond tailpipe emissions. To facilitate decision-making and planning of future infrastructural developments, the economic, social, and technological factors of ZEVs should also be addressed. Therefore, this work implements the circular economy paradigm to identify the most suitable vehicle type that can accelerate sustainable development by calculating circularity scores for Internal Combustion Engine Vehicles (ICEVs) and two ZEVs, the Battery Electric Vehicles (BEVs), and Fuel Cell Electric Vehicles (FCEVs). The circularity assessment presents a novel assessment procedure that interrelates the environmental, economic, social, and technological implications of each vehicle type on the three implementation levels of the circular economy (i.e., The macro, meso, and micro levels). The results of our analysis suggest that not all ZEVs are considered sustainable alternatives to ICEVs. BEVs scored the highest relative circularity score of 36.8% followed by ICEVs and FCEVs scoring 32.9% and 30.3% respectively. The results obtained in this study signify the importance of conducting circular economy performance assessments as planning tools as this assessment methodology interrelate environmental, social, economic, and technological factors which are integral for future infrastructural and urban planning.