Layered Extrusion of engineering Metal Alloys (LEMA) using Semi-Solid Thixotropic Feedstock

Abstract

Additive manufacturing (AM) has gained significant attention in low- and medium-volume industries due to its ability to create custom products with complex shapes, design freedom, material savings, and short lead times. While most AM processes focus on thermoplastics, there is increasing interest in metal AM systems, including powder bed fusion processes. However, these methods often involve high acquisition and operating costs, limiting accessibility. To address this, this study focuses on developing and investigating the Layered Extrusion of Engineering Metal Alloys (LEMA) system as a cost-effective alternative metal AM approach. The LEMA system manipulates alloys in the semi-solid thixotropic state. Utilising semi-solid metal slurry in extrusion-based AM can result in metal components with substantially lower operating costs and reduced thermal stresses compared to laser-based method. Experimental work initially conducted (Phase I) using the LEMA system involved in-situ creation of semi-solid thixotropic metallic alloys, particularly focusing on the Zn-Sn binary system, but improvements were made to the LEMA system for the subsequent phase to enhance performance. In Phase II, thermodynamic simulations and thermal analysis have indicated that Zn-40Sn holds promise for semi-solid thixotropic applications. Cold extrusion and heat treatment processes were employed to produce thixotropic feedstock with proper microstructures before being additively manufactured. The 3D printed components were evaluated and the result suggested that the adapted method for semi-solid billets preparation was feasible technique which then helped in a successful printing metallic material. Additionally, printing experiments were conducted to study the effects of major process parameters on the quality of deposited single-layer. It was demonstrated that single layers could be printed under 1.5 mm diameter orifice, extrusion speed of 20 mm/min, substrate moving velocity of 200 mm/min, and extrusion temperature of ≈313 ℃. The optimized printing process parameters from these experiments were then utilized for multilayer printing. It was found that substrate temperature is a key factor for achieving good metallurgical layer bonding at the interface of the printed layers. The research results support LEMA's feasibility as an alternative for the metal additive manufacturing route and lays the groundwork for processing SSMs with higher melting points in the future.