Optimization of Material Properties of selective Laser-Melted Aluminum Alloy 7075

Objectives

Objectives Experience from conventional manufacturing shows a good performance of the high-strength aluminum alloy EN AW 7075 which leads to frequent use in automotive and aerospace sector. Scientific investigations on the processability of this alloy in the SLM process shows that prepared samples have anisotropic behavior due to process-induced hot cracks (Figure 1). Furthermore, it was not possible to determine solid results regarding the fracture mechanical characterization. Due to its chemical composition, aluminum alloy EN AW 7075 has a high solidification interval. As a result, the melting and solidification of the material results in a high affinity for the formation of hot cracks. For industrial use, these hot cracks must be avoided.

Procedure

An investigation documented in literature shows that addition of 4 Wt.-% Silicon avoids hot cracking. This is due to a reduction of the thermal expansion coefficient. Furthermore another investigation shows that an increase of the pre-heating temperature of the building platform reduces the number of hot cracks in selective laser melted EN AW 7075. In practice, pure silicon is not always available for the modification of the powder, which is why a practice-oriented approach to the production of a mixed alloy made of high-strength EN AW-7075 and silica-rich AlSi10Mg is pursued in this context.

Achievements

The production of a mixed aluminum alloy based on the high-strength alloy EN AW-7075 led to process-reliable processing using SLM. When using an adequate process parameter set, the samples produced have an almost pore- free appearance without detectable hot cracks (Figure 2). A subsequent heat treatment leads to an increase in the mechanical and fracture mechanical characteristics of the mixed aluminum alloy. The approach of mixing two available powders makes it possible to compensate for negative mechanical and fracture mechanical properties and to generate additively processable material.