As one of the most important lightweight structural materials, Al-Mg alloy has been widely used in the aerospace field due to its low density, high specific strength, and high stiffness. As a new type of high-strength aluminum alloy, Al-Mg-Sc-Zr alloy offers high elastic modulus, high specific strength, and excellent damage resistance. As the aerospace manufacturing industry develops, higher performance requirements are placed on aluminum alloy structures with complex geometry. Additive manufacturing (AM) technology has significant advantages in solving such problems. This paper is designed to achieve the wide application of high-performance aluminum alloys in primary load-bearing structures in the field of aerospace and obtain additive high-strength Al-Mg-Sc-Zr alloy samples with high compactness and no porous defects.

The laser melting deposition (LMD) technology is employed to prepare samples with a size of 70 mm×10 mm×40 mm (length×width×height). The processing parameters for the deposited Al-Mg-Sc-Zr alloy samples are a laser power of 3500 W, a scanning rate of 10 mm/s, a powder-feeding rate of 0.7 r/min, a spot diameter of 4 mm, a carrier gas flow rate of 3.3 L/min, an overlap ratio of 50%, and an oxygen mass fraction ≤50×10^-6. The experimental study of LMD-processed Al-Mg-Sc-Zr alloy reveals that pores are the most important current defect in this alloy, and it is also one of the factors that greatly affects the mechanical property of the deposited Al-Mg-Sc-Zr alloy samples. In this paper, hot-rolling experiments with different reduction drafts (15%, 30%, and 50%) are conducted to weld the pores in the deposits at a later stage and thereby strengthen the alloy samples. Then, the paper further analyzed the influence of the reduction draft on the pore welding behavior, micromorphology, and mechanical property of the LMD-hot rolling (LMD-HR)-processed Al-Mg-Sc-Zr alloy.

For the wide application of the Al-Mg-Sc-Zr alloy with high performance and low porosity in primary load-bearing structures in the field of aerospace, Al-Mg-Sc-Zr alloy samples are prepared by the LMD-HR composite process. Metallographic microscopy, scanning electron microscopy, microhardness tests, and tensile tests at room temperature are conducted to explore the relationship of the composite process with microstructure and mechanical property. The optimal process parameters are determined. Then, the paper examins the influence of the hot-rolling reduction draft on the microstructure evolution, microporous defect closure behavior, and mechanical property of the as-deposited samples. The results show that the microporous defects gradually decrease with the increase in the reduction draft. When the reduction draft reaches 50%, the microporous defects are completely closed (Fig. 4). Moreover, the strength and hardness of the sample are significantly improved, and the distribution of alloy elements in the fusion line area becomes uniform. Under the optimized process parameters, the tensile strength, yield strength, elongation, and hardness of the samples prepared by the composite process are 412 MPa, 243 MPa, 23%, and 118.76 HV, respectively, which are 22.6%, 12.5%, 54.1%, and 53.3% higher than those of the unrolled samples, respectively (Fig. 9).

In this paper, bulk Al-Mg-Sc-Zr alloy samples are prepared by the LMD-HR composite process under different conditions. The effect of the hot-rolling reduction draft on the pore welding behavior, microstructure evolution, and mechanical property of the deposited samples is emphatically studied. Moreover, comprehensive factors affecting the improvement of mechanical property are clarified. The main conclusions are as follows: the composite process of HR assisting LMD can significantly improve the compactness of the deposited samples, ultimately affecting the comprehensive mechanical property of the additive workpieces. When the reduction is increased from 15% to 50%, the microporous defects tend to close gradually from a round-shape morphology as the reduction draft of the deposited sample increases. The strength and hardness of the alloy increase linearly as the reduction increases, and the hardness distribution in the deposition direction becomes more uniform gradually. Owing to the synergistic strengthening effect of porous defect elimination, work hardening effect, grain fragmentation, and fragmentation of the crystal phase at grain boundaries, the performance of the deposited samples prepared by the composite process is significantly improved. When the hot-rolling reduction draft is 50%, the average microhardness of the samples can reach (118.76±2.4) HV_0.2. The tensile strength, yield strength, and elongation are increased by 22.6%, 12.5%, and 54.1%, respectively, from 336 MPa, 216 MPa, and 14.8% in the deposition state to 412 MPa, 243 MPa, and 22.8% of the samples prepared by the LMD-HR composite process.