Page 53 - ESAM-1-2

Engineering Science in
Additive Manufacturing Multi-material additive manufacturing of metals

is validated by the hardness data presented earlier in using MM-WAAM in the longitudinal direction, Hauser
Section 3.2. et al. reported that the YS of as-built monolithic Al6060
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MS1/Cu (Type-A) and CrMn/MS1 (Type-A) was lower, and that of as-built monolithic Al5087 was
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bimetallic structures outperformed the weaker constituent higher than that of the bimetallic counterpart. Similar
trends were observed for UTS values. Upon heat treatment,
materials when compared to the earlier examples. In the all specimens—including the bimetallic—experienced
MS1/Cu system, specimens fabricated at various scanning improved YS and UTS as expected. The UTS of the heat-
speeds showed similar UTS and elongation, except for treated bimetallic structure was comparable to that of
the one built at 1,250 mm/s. At this higher scanning Al6060 and slightly lower than that of Al5087, confirming
speed, a fracture occurred at the interface rather than on the beneficial influence of post-processing on mechanical
the Cu side, which had been the fracture location in all performance. Consistent with earlier observations, porosity
other specimens (Figure 11B). As previously discussed and defects negatively influenced mechanical properties in
in Section 3.1 (Figure 8G), the MS1/Cu interface at low Al/Cu bimetallic structures. In contrast, Al/Al bimetallics,
scanning speeds exhibited good metallurgical bonding similar to other same-element combinations (e.g., CrMn/
due to enhanced thermal conductivity and Marangoni MS1-Fe/Fe and Ti-5Al-2.5Sn/Ti-6Al-4V–Ti/Ti), exhibited
convection. These effects, influenced by Cu and Fe good metallurgical bonding and superior mechanical
dissolution, contributed to the solid-solution strengthening performance compared to wrought material or monolithic
of the Cu at the interface. In the CrMn/MS1 bimetallic as-built materials.
structure, specimens exhibited slightly higher tensile
strength compared to wrought CrMn, but lower than AM 4.3. Flexural strength
MS1. The fracture occurred on the CrMn side, indicating Compared to other mechanical properties, the flexural
good metallurgical bonding. As with earlier observations, strength of MMAM structures has received relatively
tensile strength and elongation were influenced by process limited attention. Among the available literature, ferrous-
parameters, indicating that optimal scanning conditions based MMAM structures such as C300MS/AISI304 and
can promote ideal metallurgical bonding. Notably, CrMn/ C300MS/AISI1045CS, fabricated in Type-A and Type-D
MS1 exhibited better tensile strength than wrought CrMn orientations (Figure 9), have shown promising results.
due to its improved bonding. Interestingly, bimetallic Both bimetallic structures exhibited higher flexural YS
structures composed of the same alloy system but with and Ultimate flexural strength (UFS) compared to their
different compositions (e.g., Ti-5Al-2.5Sn/Ti-6Al-4V) monolithic counterparts. Notably, while the UFS of
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demonstrated better tensile behavior than the weaker C300MS/AISI1045CS was 9.2% lower than that of its base
monolithic constituent. This could be attributed to good material AISI1045CS, the C300MS/AISI304 specimen
metallurgical bonding and a defect-free interface. exceeded its monolithic counterpart by 2.5% (Figure 12).
Similar to the other same-alloy bimetallic structures, This suggests that interfacial strengthening in C300MS/
the AlSi10Mg/C18400 (Type-D) specimen exhibited AISI304 is more effective, likely due to coherent grain
higher tensile strength than C18400, but significantly lower orientation bridging across the interface, which enhances
than AlSi10Mg. Failure predominantly occurred on the load transfer and structural integrity.
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Cu-rich side, reinforcing the notion that interfacial bonding A similar interfacial effect was observed in MS1/Cu
between Al and Cu is stronger than the bonding within MMAM structures fabricated using LPBF in the Type-A
the Cu-rich region itself. Fractographic analysis revealed orientation (Figure 9) under varying scanning speeds.
a mixed brittle and ductile fracture mode, with ductile The flexural strength varied significantly, attributed to the
features dominating. This was influenced by the presence presence of defects and suboptimal processing conditions.
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of unmelted particles on the Cu side of the fracture surface, Among the tested parameters, a moderate scanning speed
which acted as stress concentrators and initiated failure. of 800 mm/s yielded the highest UFS of 557 ± 19 MPa, due
Similarly, tensile testing of Al12Si/Al3.5Cu1.5Mg1Si to strong interfacial bonding and defect-free (Figure 12B
(Type-A) revealed a higher YS of 267 ± 10 MPa compared [regarding flexural strength] and Figure 8G and H
to as-built LPBF bulk counterparts. However, the UTS was [regarding interfacial morphology]). Beyond the influence
lower than that of the bulk materials due to differences in of process parameters, IBL additions can also affect the
microstructure. Fractographic analysis revealed a brittle flexural properties of the MMAM structures. In SS316L/
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fracture mode approximately 200 μm from the interface CuSn10 and CuSn10/SS316L, the flexural strength differed
on the Al12Si side, indicating good metallurgical bonding due to the incorporation of tin–bronze (TB). Specifically,
accompanied by localized embrittlement. Finally, for the the addition of TB flexural strength by 20% in both
Al6060/Al5087 (Type-A) bimetallic structure fabricated configurations. 58,142 Despite this reduction, both structures

Volume 1 Issue 2 (2025) 21 doi: 10.36922/ESAM025180010