Investigating The Effect of Coating Material, Thickness and Joint Configuration on Mechanical Property of Welded Mild Steel
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Date
2024-05
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Addis Ababa University
Abstract
The influence of coating material, thickness and joint configuration on mechanical property of SMAW
welded joint for SAE1020 mild steel was assessed in this study. The coating material has 2 levels zinc
and copper with 4 different coating thickness levels 85-95, 100-110, 115-125 and 130-140 with 2
welding configuration butt and lap joint. The design of experiment (DOE) was done using taguchi
orthogonal array then for the mixed level taguchi design array L16 (4^1 2^2) experimental runs were
conducted. During welding coated mild steel there is a trapping of zinc and copper in molten pool of
steel causing mechanical property reduction and welding defect on microstructural analysis.
This work investigates mechanical properties namely hardness, tensile and flexural strength of welded
joint under different coating material, thickness and joint configuration. In addition to this the micro
structure analysis of welding zone of uncoated and coated with 85-95 and 130-140 coating thickness
was analyzed using an optical microscope with 100* magnification.
The result of the investigation indicates that significant decrease in hardness with increase in coating
thickness. From the experiment with increasing the coating thickness from 85 micro meter to130 micro
meter the hardness value decrease with 15.55% and in joint configuration butt joint configuration
reduced with 1.605% compared to lap joint. The tensile strength and flexural strength is lower with
9.21% and 8.9% with increasing coating thickness from 85 micro meter to130 micro meter. The optimal
parameter set are 85-95 coating thickness, copper coating material and butt joint configuration this was
analyzed using grey relation analysis. The signal-to-noise ratio rank conclude that Varying the coating
thickness found to cause more significant changes on mechanical properties than varying coating
material and joint configuration. The micro structural investigation of uncoated and coated mild steel
was done using an optical microscope. The result of the investigation indicates that a weld
ing defect was seen in microstructure of zinc coated mild steel as coating thickness increase. in addition
to this in the fusion zone of the welding there is a small increase in grain size then this will reduce the
strength of material. Finally uncoated mild steel shows better mechanical property than the coated one
but for some critical reasons if coated mild steel is used this work recommend to use a mild steel with
coating thickness of 85-95 for safe and quality structural construction.
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Keywords
Mild steel, Coating thickness, Coating material, Small scale copper and zinc coating technique, mechanical properties.