Analysis on Mechanical Properties and Corrosion Behavior of Friction Stir Processing of Commercially Pure-Titanium

Abstract

Abstract Friction Stir Processing has become the ideal way to refine the grains which increases the mechanical properties like formability, microhardness, yield strength and Tensile Strength, also increases the corrosion resistance, which emerged as the effective way for selective surface modification and also retaining the bulk properties. In this present work, Titanium grade 2 (Commercially Pure Titanium) is selected as the material of choice due to its superior corrosion resistance compared to other grades of titanium, high tensile strength and high hardness. Due to soft, excellent corrosion resistance and ductile properties Cp - Ti is used in automotive parts and airframe structure application. Friction stir processing is being used to improve mechanical properties such as tensile and microhardness, as well as corrosion properties. Friction stir processing (FSP) is used to fabricate the Titanium plate, by varying the process parameters such as Tool Rotation Speed (rpm), Traverse Speed (mm/min), and Number of Passes. The process parameters used in this experiment are Tool Rotational speed of 1000 rpm, 1200 rpm and 1400 rpm, Traverse speed of 30 mm/min, 45 mm/min, and 60 mm/min and single pass, double pass and triple pass. Taguchi’s L9 Orthogonal array is used to conduct the experiment, which considers three parameters at three separate levels. A tapered cylindrical pin of HSS (High Speed Steel) with Rockwell hardness of 65 HRC is designed and fabricated to provide material flow while simultaneously minimizing the tool wear. The tensile test was carried out using Universal Testing Machine (UTM) as per ASTM E8 standard to determine the ultimate tensile strength and yield strength of FSPed CP – Ti (grade 2), microhardness test was carried out using Vickers Hardness with a diamond indenter and corrosion values are evaluated using Immersion corrosion testing method by weighing the before and after weights of the sample as per ASTM G31 – 72. Since Titanium Grade 2 offers very high corrosion resistance, the rate of corrosion is negligible when done in 24 hours. Thus, immersion corrosion test is done over 120 hours, so that corrosion rate can be measured efficiently. And also evaluate the torque induced in this process. Grey Relational Analysis (GRA) is performed on the multiple test results such that tensile strength, microhardness and corrosion resistances to find the optimum process parameters, by applying the test results as inputs. Analysis of variance (ANOVA) is the most efficient parametric method for analyzing friction stir processing data from experiments results.