Microstructure and Mechanical Properties of Wire + Arc Additively Manufactured Mild Steel by Welding with Trailing Hammer Peening

Abstract

The microstructure of the parts manufactured by Wire Arc Additive Manufacture (WAAM) is dominated by columnar grains with large size, [1][2][3][4][5] which seriously affects the service performance and life of the parts. [2,[5][6][7] There are two kinds of viable approaches to improve the microstructure of the welds produced by Additive Manufacturing (AM): adjusting the welding process parameters [8][9][10][11][12][13] and introducing external auxiliary means. [14][15][16][17][18][19][20][21] The formation of "AMþ" hybrid AM technology by introducing external auxiliary means to assist the AM has shown good effect and prospect in solving the problem, especially the introduction of specific kinds of energy field such as the mechanical force-energy field, [14][15][16] the ultrasonic field, [17,18] the laser-energy field, [19] and the electromagnetic field. [20,21] However, the mechanical force-energy field-assisted AM technology has attracted much more attention of researchers in the researching field, for the reason of owning the following advantages: a remarkable effect, simple equipments, lower cost, and strong reproducibility, as well as a great potential in academic research and engineering application. [15,16] The interlayer rolling is the most commonly used WAAM technique assisted by mechanical forceenergy field in current researches. [1,2,[4][5][6]16,[22][23][24][25][26][27][28][29][30] The technique is equipped with heavy equipment to generate continuous rolling static pressure up to thousands of newtons. The large static pressure can drive the roller to introduce continuous and uniform plastic deformation in the additive layers which can improve the microstructure and mechanical properties of the additive layers. [16,30] Many researchers [1,2,5,16,25,26] have used this kind of technique to process different metal additive layers, studied the influence on the microstructure evolution of the additive layers under the process, and finally, revealed the influence mechanism of the microstructure evolution of the additive layers on the mechanical properties under the process.Interlayer hammer peening is another novel WAAM technique proposed in recent years, [15] which need not be assembled with heavy equipment to provide greater continuous static pressure but can combine with industrial robots well, so as to achieve a higher processing freedom. [15,31] This technique provides some new thoughts and directions for exploring and expanding the new style of "AMþ" hybrid AM technology. Different from the interlayer rolling technique, the interlayer hammer peening technique has the following characteristics: 1) the acting force is instantaneous impact force with the very short acting time, and the instantaneous contact force is great with high plastic

Directed energy deposition + mechanical interlayer deformation additive manufacturing: a state-of-the-art literature review

“…Xiong et al [110], low-alloy steel (AWS ER70S-6) DEDed-laser + interlayer hot hammer peening, also observed the parent phase (γ) dynamic recrystallization at the layer surface; however, due to the γ → α transformation, the final microstructure is not significantly affected. Although the prior γ grain size affects material hardenability and α formation/morphology, the mandatory effect on the final microstructure is governed by the cooling rates [165], which is almost insensible to the interlayer hot hammer (low effect on geometric aspects of the deposited layer) [110]. Thus, the interlayer hot hammer peening for transformable alloys showed insufficient grain refinement that justified its use.…”

“…Ye et al [108] (DED-laser) and Li et al [109] (DEDlaser) developed a hot ultrasonic micro-forging system with an operating frequency of 20 kHz; Xiong et al [110] (DEDarc), a hot hammer penning system with an operating frequency of 21 Hz. These systems [108][109][110] (Fig. 12) resemble the cold hammer previously shown in Fig.…”

Finite element simulation of residual stress of wire arc additive manufactured low alloy high strength steel component assisted by interlayer hammering

“…The horizontal tensile property is the best when the interlayer is hammered three times. Xiong 17 found that hammering can improve the mechanical properties of the near-surface layer of the mild steel weld and improve the strength of the weld in the study of wire+arc additively manufactured mild steel by welding with trailing hammer peening. Zou 18 demonstrated by finite element simulations that hammering could effectively reduce residual stress in welds.…”

A benchmark of mechanical properties and operational parameters of different steel filler metals for wire arc additive manufacturing

“…Average tensile properties of WAAM ER70S-6 reported in literature[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][35][36][37][38][39][40][41][42]44,45].…”