Development of low cost,non-flammable and high strength magnesium alloys using liquid forging and extrusion

• Main Author: Nagarajan Venkatakrishnan
• Other Authors: Tan Ming Jen
• Format: Theses and Dissertations
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/66368
• Institution: Nanyang Technological University

In today’s world, there is an increasing demand for light weight, high-strength structures in engineering applications for the aerospace, automotive, semiconductor and marine industries. Though many lightweight metals are being used, the most effective of them is magnesium. It is the lightest of all structural metals available due to its low density value. AZ-91 cast magnesium alloy is one among the most commonly used in the industry as it is the most economical in terms of material cost and processing cost. But the major drawbacks of the alloy are its high flammability issue at high temperatures and poor corrosion resistance and mechanical properties. This project aims at the development oflow cost, non-flammable and high strength magnesium alloy from AZ-91 magnesium alloy by alloying it with elements like Ca, Ce and incorporating the processes of liquid forging and extrusion to obtain high ignition resistance as well as good mechanical properties. The process parameters of liquid forging and extrusion were carefully studied to analyze their influence on the ignition and mechanical properties of the developed alloy. Furthermore, metallographic analysis and tensile tests were conducted to evaluate the quality of the manufactured alloy. From the results, it was evident that the addition of low cost element such as Ca and combined addition of Ca and Ce have considerable effect on the ignition resistance and mechanical properties of the alloy. With the increase in addition of Ca content in the alloy, the mechanical properties of the liquid forged AZ91 alloy were reduced. This was overcome by introducing the process of extrusion whereby the properties of the alloy were enhanced with increasing Ca addition to a certain extent. For example, the ultimate tensile strength of the liquid forged AZ91-4Ca sample was 172 MPa, about 11% higher than the gravity cast sample with ultimate tensile strength of 153MPa. The extruded sample exhibited a much higher value of UTS of about 373MPa which was about 53% higher than the liquid forged sample, hi the same manner, the yield strength and elongation of extruded AZ91-4Ca was 70% and 34% higher than the liquid forged samples, hi terms of ignition resistance properties, the ignition temperature of the pure AZ91 alloy was about 544 °C. With the increase of Ca addition in the alloy, the ignition temperature of the alloy was increased. For AZ91 added with 8% Ca content, the ignition point was about 884 °C, which was 38.5% higher than the ignition point of pure AZ91 alloy.