ASHOKA VARTHANAN P
Dean-Innovation and Professor
Head of Mechanical Engineering Department
Sri Krishna College of Engineering and Technology, Kuniamuthur, Coimbatore.

SHOT PEENING PROCESS TO IMPROVE THE FLEXURAL STRENGTH OF HEATED 2024 ALUMINIUM ALLOY
Shot peening (SP) is form of cold working process used to impart residual compressive stress (RCS) layer over the metal surface. This RCS modifies the mechanical properties of the metals and composites. It is a process in which the spherical shot materials are forced to bombard on the target material by means of controlled air pressure or through other means. This in turn creates a plastic deformation on the metal surface called dimples resulting in the RCS. One of the main objectives of SP is to prevent micro crack propagation on the material surface. The imparted RCS arrests the micro crack propagation on the material surface and avoids premature failure. Moreover, SP enhances the properties of the base metal, viz, flexure, fatigue, surface hardness and corrosion resistance (based on the type of peening material). SP is widely used to strengthen and relive stresses in components like springs, crankshafts and connecting rods. Research shows that SP ofAA2024 in optimum conditions using ceramic, glass beads, steel and nickel shots increases its fatigue life. SP of aluminium alloy 2024 using nickel shots increases the flexure, fatigue and surface hardness of the material. Other than compressed air peening, centrifugal peening, ultrasonic peening, wet peening and laser peening also improves the properties of the base metal. In this research, hot shot peening (HSP) is carried out for the first time. The base metal AA2024 is heated to 300 0 C in muffle furnace and then it is shot peened using spherical steel shots even before the sample pieces are cooled. The temperature for heating is chosen well below the recrystallization temperature of aluminium alloys. Shot pressure and distance are considered as the input parameters and the experiments are conducted. Flexural strength is obtained for the best peening pressure and distance. Confirmation experiments are carried out and the results are compared with unpeened and non-heat treated specimen. It is confirmed that the flexural strength of heated and shot peened AA2024 specimen improved by 12.83 % than the unpeened specimen.