EFFECT OFAGEING ON MECHANICAL AND FATIGUE BEHAVIOUR OF 2014 ALUMINIUM ALLOY

Abstract

This work deliberates the influence of ageing on Mechanical and Fatigue properties of Aluminium alloy 2014T6. In addition, the influence of ageing on micro-structure is also considered using Optical Microscopy, Scanning Electron Microscope (SEM) and X-ray Diffraction. Experiment begins with solution treatment to the as received Aluminium alloy 2014 T6 (industrial available) at temperature 504°C. Solution treatment restore any microstructure alterations present. Quenching followed by solution treatment locks the microstructure of AA2014 in Super saturated meta-stable state. Subsequently, ageing treatment was completed at three different temperatures and four different time periods. No significant variations detected in mechanical and fatigue properties for ageing temperature of 130°C. however a decent hike was observed for ageing at temperature 160°C. The raise was continuous up to 10Hour of time period. Ultimate Tensile Strength and Yield Strength for this ageing parameter was 490MPa and 440MPa with an increase of about 35% and 50% respectively. An increase in fatigue behaviour was also observed till 8Hour of ageing after that a deleterious effect was noted. However, ageing has a deleterious effect on material elongation properties. Exploring microstructure with different tricks shows nucleation and growth of different phases while ageing of alloy. SEM, EDX and XRD plots of differently aged samples discloses that as the number and size of the phases increases the material strength increases too. Examining the crack through Optical and SEM reveals the deviation of crack path from straight line to zig-zag along with ageing. Investigations concerning crack path reveals that zig-zag path are the mark of increase in fatigue resistance. The deviations are due to the presence of hard phases nucleated during ageing. Ageing at 190°C shows increase in material strength for a while later on it has a deleterious effect on mechanical properties. This may be a result of over ageing of the alloy. The number and sizes of the phases present in these cases are relatively larger than 160°C ageing.