CuMn13Al7 Additive Manufacturing Forming Characteristics
Figure 1 shows a sample of the CuMn13Al7 thin wall printed by arc additive manufacturing technology. It can be seen from the sample picture that the thin-walled CuMn13Al7 printed by the CMT power supply is adequately formed without collapse, and the welding wire splashing is small during the forming process. In addition, from the sample cross-sectional view (metallographic sample) given in Figure 2, it can be seen that there are almost no defects inside the sample and that the metallurgical bonding is good, which further illustrates that CuMn13Al7 has good forming performance by arc additive manufacturing.
High-Manganese Aluminium Bronze CuMn13Al7 Additive Manufacturing Composition and Microstructure Characteristics
Table 3 shows the chemical composition analysis results of the high-manganese aluminium bronze CuMn13Al7 arc additive manufacturing samples. Compared to the chemical composition of the raw silk materials given in Table 1, it can be seen that the main alloying element Mn in the arc additive manufacturing sample has a burning loss of 6.1%. The decrease in relative content is more pronounced, which indicates that the arc additive manufacturing process has better protection and better deoxidation performance in the molten pool.
Figure 3 is an X-ray diffraction (XRD) pattern of a high-manganese aluminium bronze CuMn13Al7 arc additive manufacturing sample, and the main phase composition of the sample is Cu0.69Al0.28Ni0.02 and Cu.
Figure 4 shows the metallographic pictures of the high-manganese aluminium bronze CuMn13Al7 arc additive manufacturing samples at different locations. The low magnification metallographic structure is shown in Figure 4a, and the equiaxed crystal region is shown below that. The entire sample is mainly composed of equiaxed crystal regions, and there are fewer columnar crystals. The middle strip is the remelting zone, and the heat-affected zone is above the remelting zone. From Figures 4b and c, it can be seen that the metallographic structure of the equiaxed grain region of the high-manganese aluminium bronze CuMn13Al7 arc additive manufacturing sample is α + β + point phase, and the grain boundary α is obvious. The sample metallographic structure in the remelting zone is α + β + point phase with no obvious grain boundary α (see Figures 4d and e). The metallographic structure of the sample heat-affected zone is α + β + dot-like phase, and the grain boundary α is weaker than that in the equiaxed grain region (see upper part in Figures 4d and f). In addition, it can be seen from the low magnification metallographic photograph in Figure 4a that no cracks, holes, solid inclusions, unfused, unwelded, poorly shaped or sized, and other defects are found, indicating that the internal quality of the CuMn13Al7 steel arc additive manufacturing is good. Figure 5 shows a high magnification SEM image of the metallographic sample. No small defects were found in the high magnification SEM image. The sample mainly had a fine needle-like structure inside the equiaxed crystal region under high magnification SEM.
To further analyse the crystal structure of the high-manganese aluminium bronze CuMn13Al7 arc additive manufacturing sample, Figure 6 shows the TEM image of the sample and the EDS composition of the corresponding particles. From the TEM image (Figure 6a), it can be seen that there is a granular reinforcing phase in the slab-like matrix of the sample crystal structure at high magnification. The EDS analysis results corresponding to Figures 6b–e show that the main elemental composition of the large particle reinforcing phase is Fe, Mn, Al, and the main elemental composition of the small particle reinforcing phase is Cu, Mn, Fe, Al. The light and dark matrix phases are mainly composed of Cu, Mn, Al, and Fe, which are consistent with the elemental composition of the samples obtained by chemical analysis.
Figure 7 shows the crystal structure and corresponding selected area electron diffraction pattern of the high-manganese aluminium bronze CuMn13Al7 arc additive manufacturing sample. Figure 7a is a high-magnification image of the large particle enhanced phase in Figure 6a and the corresponding selected area electron diffraction pattern. From the analysis of the pattern, it can be seen that the corresponding phase is the Fe2MnAl phase. The EDS elemental composition results of the large particle enhanced phase are consistent, but there is no obvious Fe2MnAl phase diffraction peak in the XRD pattern of the sample in Figure 3. This may be attributable to the fact that XRD analysis is generally considered for phases with a relative content of less than 5%. The diffraction peak is not seen clearly in the entire spectrum, so no Fe2MnAl phase was found in the XRD pattern of the sample. Figure 7b shows the morphology of the matrix phase and the corresponding selected area electron diffraction pattern. From the analysis of the results, it can be seen that the corresponding phase is Cu0.69Al0.28Ni0.02, which is in accordance with the XRD (Figure 3) results and the figure of the sample. The results obtained from the analysis of Figures 6c and e are also completely consistent in this regard. In addition, TEM analysis revealed that particle-reinforced phases + twins (Figure 8a) and particle-reinforced phases + dislocations (Figure 8b), particle-reinforced phases, twins, and dislocations also existed in the sample. The appearance of such components is beneficial for increasing the strength of the sample.
Performance of High-Manganese Aluminium Bronze CuMn13Al7 Additive Manufacturing Samples
Figure 9 shows the microhardness distribution of the high-manganese aluminium bronze CuMn13Al7 arc additive manufacturing samples. During the test, measurements are obtained from the upper part of the weld (2 mm) to the lower part, and from the left (2 mm) to the right. Results were obtained at 10 uniformly spaced points (1 mm apart). From the microhardness distribution chart, it can be seen that the hardness distribution of the high-manganese aluminium bronze CuMn13Al7 arc additive manufacturing sample ranges from 173 to 220 HV0.1, and the hardness distribution is relatively uniform. The average microhardness of the longitudinal cross section of the sample is 192.7 HV0.1, the average microhardness of the transverse cross section of the sample is 190.5 HV0.1, and the difference between the average microhardness of the longitudinal and transverse cross sections is small. The fluctuation of the microhardness is mainly caused by the change in the microstructure. From the cross-sectional morphology of the high-manganese aluminium bronze CuMn13Al7 formed sample produced by arc additive manufacturing shown in Figure 2, it can be seen that the formed sample is a multi-layer and multi-pass surfaced structure. The effects of thermal cycling of the weld bead generally includes the original columnar crystal zone, remelting zone, and heat-affected zone. Different regions have different microhardness values owing to different microstructures (grain size, precipitates, etc.), so the sample cross-section hardness is expected to fluctuate by nominal amounts.
The test results of the mechanical properties of the high-manganese aluminium bronze CuMn13Al7 arc additive manufacturing sample are shown in Table 4. Figure 10 shows the tensile curve of the CuMn13Al7 sample made by wire arc additive manufacturing. From the results, it can be seen that the sample has excellent mechanical properties, yield strength of 301 MPa, tensile strength of 633 MPa, elongation of 43.5%, reduction in area of 58%, and Charpy impact value of 68 J/cm2 at − 20 °C.
In order to analyse the fracture mechanism of the sample, Figure 11 shows the tensile fracture morphology of the high-manganese aluminium bronze CuMn13Al7 arc additive manufacturing sample. It can be clearly seen from the overall morphology of the tensile fracture in Figure 11a that there are no obvious defects in the tensile specimen, which is in accordance with the experimental results of the tensile elongation and section shrinkage of the tensile specimen, as shown in Table 4. Figures 11b, c, and d are the morphologies of the tensile fracture fibre zone, radiation zone, and secondary fibre zone, respectively. From the figure, it can be seen that there is a large number of dimples in the fracture, indicating that the sample is stretched. The fracture mechanism is mainly ductile fracturing, and the radiation area has a river-like dissociation surface morphology.
Figure 12 shows the kinetic potential polarisation curve of the sample. It can be seen from the figure that the anodic polarisation curve of the sample is divided into two distinct stages. The anode current density rapidly increases in the interval between the corrosion potential (EC) and point A, indicating that no obvious passivation behaviour has occurred on the sample surface. Controlled by activation and mass transfer processes, the maximum current and slower increase of current in the interval A ~ B indicate that the reaction in this interval is controlled by the mass transfer process. The corrosion potential and corrosion current density of the samples obtained by software fitting are shown in Table 5. Figure 13 shows the corrosion morphology of the sample after the potentiostatic polarisation test. It can be seen from the figure that the electrochemical corrosion mechanism of the sample is mainly intergranular corrosion.
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