Influence of Adding Modifying Elements and Homogenization Annealing on Laser Melting Process of the Modified AlZnMgCu with 4%Si Alloys

Abstract

AlZnMgCu, the high-strength aluminum alloy, is unsuitable for laser melting applications due to its high hot cracking sensitivity and large solidification temperature range. Adapting this alloy for laser melting processing is a high-demand research issue for extending its use. Thus, this paper investigates the effect of adding 4%Si, 4%Si-Sc+Zr, 4%Si-Ti+B, and homogenization annealing on the laser melting process (LMP) of AlZnMgCu alloy. Homogenization annealing at 500 °C for 6.5 h was selected to dissolve most of the low melting temperature phases into the grain matrix and perform stable alloys for the LMP. The pulsed laser melting process (PLM) was performed on the as-casted and the homogenized samples. The microstructures of the as-casted, the homogenized alloys, and after the LMP were evaluated. In addition, the hardness of the base metal (BM) and laser melted zone (LMZ) were measured. The results revealed that the microstructure was enhanced and refined in the as-cast state by adding the modifiers due to the increasing nucleation potency of solidification sites and the formation of primary Al3(Ti, Zr, Sc) phases. The average grain size was decreased by 15.6 times when adding 4%Si + 0.4%Zr + 0.29%Sc, while it decreased by 10.2 times when adding 4%Si + 1%Ti + 0.2%B. The LMZ of the as-casted samples exhibited a non-uniform distribution of the grains and the elements after the LMP. This was attributed to the evaporation of Zn, Mg during the high laser power process besides the non-uniform distribution of elements and phases in samples during casting. After the laser treating of the homogenized samples with 4%Si-Sc + Zr, uniform columnar grains were formed in the direction of the laser. The presence of Ti and B changed the crystallization nature, resulting in the LMZ with very fine and equiaxed grains due to forming many nucleation centers during solidification. The hardness values have positively increased due to Si addition and adding a combination of Ti + B and Sc + Zr. The maximum hardness was 153.9 ± 5 HV achieved in the LMZ of the homogenized samples of 4%Si + 1%Ti + 0.2%B.

The influence of the modifying elements on the microstructure, mechanical, and deformation properties of aluminum alloys

“…the modified alloy, the presence of Ti-B resulted in an equiaxed dendritic structure surrounded by the eutectic phases (Figures2B, 3B, 4B). The main reason for the refinement of the dendritic structure is the presence of the heterogenous enucleation centers TiB 2 and Al 3 Ti which in agreement with(Mosleh et al, 2021).…”

Novel Assessment Methodology for Laser Metal Deposition of New Metallic Alloys

“…Therefore, the methodology developed in the work was adequate to avoid hot cracking in the AA7075 alloy. The melting of AA7075 alloy without hot cracking was previously reported in the literature [ 27 ], but the composition of the standard alloy was modified by the addition of different amounts of Si and other alloying elements.…”

“…However, the microstructural analysis revealed the presence of solidification cracks. Mosleh et al [ 27 ] also investigated the effect of adding modifying elements to as-cast AA7075. They conducted the melting of three different casted alloys that included, in all cases, 4% Si.…”

The Effects of Zirconium and Yttrium Addition on the Microstructure and Hardness of AlCuMgMn Alloy when Applying In Situ Heating during the Laser Melting Process

“…However, selective laser melting (SLM), which is a process that is similar to the welding process, has several substantial limitations when processing high-strength Al-Cu-Mg alloys such as AA2024 [12][13][14][15][16]. As a result of the melt pool's rapid melting and rapid cooling, cracking happens when large residual thermal stress and temperature gradients appear in SLM specimens [10,[17][18][19][20].…”

“…At these temperatures, cracking begins when thermal tensile stresses reach the limit of the endurable strain essential to form a crack during solidifying [17]. Rapid solidification and high cooling rates can cause solidification cracking in Al alloys, according to recent research on the laser cracking susceptibility of this material [16,[24][25][26]. The second way to control the solidification cracks for this alloy is by preheating the samples before laser processing.…”