Paul Rometsch’s research while affiliated with Centre for Ecology Development and Research and other places

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Publications (32)


Laser-Based Additive Manufacturing Processability and Mechanical Properties of Al-Cu 224 Alloys with TiB Grain Refiner Additions
  • Article
  • Full-text available

January 2025

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25 Reads

Materials

Esmaeil Pourkhorshid

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Paul Rometsch

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X-Grant Chen

This study investigated the impact of TiB grain refiner additions on the microstructural evolution, hot tearing susceptibility, and mechanical properties of Al-Cu 224 alloys to enhance their processing performance during the selective laser melting (SLM) process. A simple laser surface remelting method was utilized to simulate laser-based rapid solidification. The results revealed that the addition of appropriate amounts of TiB grain refiner could completely eliminate the solidification cracks during the laser surface remelting process. The introduction of TiB2 particles in the melt pools through the TiB grain refiner addition changed the grain morphology from a coarse columnar to a fine equiaxed structure, and the grain sizes were reduced from 13 to 15 μm in the base alloys to 5.5 μm and 3.2 μm in the alloys with 0.34 wt% Ti (B-3TiB) and 0.65 wt% Ti (ZV-6TiB) additions, respectively. The hardness values of the modified B-3TiB and ZV-6TiB alloys reached 117 and 130 HV after a T6 heat treatment, which surpassed the hardness of conventional AlSi10Mg alloys by at least 15–30%. This improvement was attributed to the finer grains and nanoscale θ′/θ″ precipitates. The results demonstrate that the TiB grain refiner addition can significantly improve the processability and mechanical properties of Al-Cu 224 alloys for SLM applications, offering a promising solution to the challenge of high hot tearing susceptibility in high-strength aluminum alloys.

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Evolution of mechanical properties and microstructure of selective laser melted AlSi10MgMn alloy with different post heat treatments

September 2024

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35 Reads

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1 Citation

Materials Science and Engineering A

This study investigated the effects of various post heat treatments on the mechanical properties and microstructure evolution of an AlSi10MgMn alloy containing 0.5 wt% Mn produced by the selective laser melting process for the first time. The microstructures under different conditions were analyzed using optical microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. In the as-manufactured (F) condition, the alloy exhibited an ultimate tensile strength (UTS) of 486 MPa, a yield strength (YS) of 299 MPa, and an elongation of 10.3 %. After a T5 treatment, the UTS and YS increased to 532 MPa and 386 MPa, respectively, resulting in a remarkable 30 % improvement in YS compared to the F state. The tensile properties achieved by the new alloy were considerably higher than those reported for conventional AlSi10Mg alloys in the F, T5, and T6 conditions. The T5 treatment promoted the precipitation of a large fraction of Si-rich nanoparticles and MgSi-based precipitates without disrupting the Si-rich network. After a T6 treatment, the Si-rich network completely disappeared, and the main strengthening phase was MgSi-based precipitates accompanied by α-Al(Mn,Fe)Si dispersoids induced by the Mn addition. Using microstructure-based constitutive models, the strengthening contributions of various microstructural components to mechanical strength in different processing conditions were analyzed.


Microstructure evolution of the three alloys during homogenization. a, b, c SEM images showing the distributions of particle zones (PZ), particle-free zones (PFZ), and intermetallic compounds (IMCs) for (a) base AA5083, (b) 0.05Sc + 0.08Zr, and (c) 0.1Sc + 0.08Zr alloys; (d–f) bright-field TEM images showing the precipitation of Mn-dispersoids for d base AA5083, e 0.05Sc + 0.08Zr, and f 0.1Sc + 0.08Zr alloys; g TEM-EDS analysis of Mn-dispersoids; h,i dark-field TEM images showing the characteristics of L12-Al3(Sc,Zr) precipitates for (h) 0.05Sc + 0.08Zr, and (i) 0.1Sc + 0.08Zr alloys.
Thermomechanical processing routes for the different tempers.
Stress–strain curves and tensile properties for all alloys and tempers, a true stress–strain curves, b yield strength, c ultimate tensile strength, and d elongation to fracture.
Effects of Sc and Zr additions on VDA bendability in O- and H321-tempers.
Bright-field TEM images a, b, c showing the distribution of Mn-dispersoids, and dark-field TEM images d, e showing the distribution of L12-Al3(Sc,Zr) precipitates for the three alloys in the O-temper: (a) base, (b, d) 0.05Sc + 0.08Zr, and (c, e) 0.1Sc + 0.08Zr alloys.

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Mechanical and corrosion performances of Al–Mg-Mn 5083 rolled alloys microalloyed with Sc and Zr in different thermomechanical processing conditions

July 2024

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60 Reads

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1 Citation

Journal of Materials Science

The mechanical properties, corrosion behavior, and related microstructures of Al–Mg-Mn AA5083 rolled sheets microalloyed with Sc and Zr were investigated under various thermomechanical processing conditions. The results revealed that adding 0.05 wt.% Sc resulted in a minor change in the alloy performance relative to the base alloy. When the Sc content reached 0.1 wt.% it significantly improved the alloy strength and recrystallization resistance, and dramatically lowered the intergranular corrosion (IGC) susceptibility. Compared with the base alloy, the 0.1 wt.% Sc addition (along with 0.08 wt.% Zr) increased the yield strength (YS) by 8, 75, 25, and 33% for the cold-rolled (H18-), annealed (O-), extra-deformed (H116-), and stabilized (H321-tempers) conditions, respectively. In addition, the recovery and recrystallization resistances were significantly improved, as demonstrated by the retained deformed fibrous structure in the O- and H321-tempers. Furthermore, the IGC susceptibility was substantially decreased in the H321-temper due to the prevention of continuous β-Al3Mg2 precipitation along recrystallized grain boundaries. The YS of the final rolled sheets was modeled using constitutive analysis to predict the effects of various microstructural components on the strengthening contribution. Graphical Abstract


Impact of hot rolling temperature on the mechanical properties and microstructural evolution of hot/cold-rolled AA5083 with Sc and Zr microalloying

March 2024

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71 Reads

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5 Citations

Material Science and Engineering

The impact of hot rolling temperature on the microstructure evolution and mechanical properties of hot/cold rolled AA5083 alloy containing Sc and Zr was studied. The results revealed that low hot-rolling temperatures (LHRT: 400–425oC) resulted in superior tensile properties compared to high hot-rolling temperatures (HHRT: 500–525 oC). The yield strength (YS) of the LHRT samples reached 450 MPa in the H18-temper and 291 MPa in the O-temper, which were respectively 20% and 39% higher relative to the HHRT samples. Microalloying with Sc/Zr and two-step homogenization promoted the formation of dispersed particles in the form of Mn dispersoids and nanosized Al3(Sc,Zr) precipitates. The rolling temperature was found to have a profound impact on the characteristics of these dispersed particles and on the recrystallization resistance. The HHRT caused the coarsening of both dispersed particles during rolling. The LHRT preserved the deformed elongated grain structure due to a stronger retardation of recovery and recrystallization during hot rolling and post-annealing. The strengthening mechanisms of the Mn-dispersoids and Al3(Sc,Zr) precipitates were quantitatively analyzed based on particle characteristics. The predicted YS contributions in the O-temper were in good agreement with the measured YS difference between the LHRT and HHRT samples.


Hot Deformation Behavior and Post-brazing Grain Structure of Dilute Al–(Sc–Zr) Alloys for Brazed Heat Exchangers

February 2024

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19 Reads

An abnormally coarsened grain structure after brazing can negatively affect the in-service performance of a brazed heat exchanger. One of the numerous beneficial effects from the Sc addition to aluminum is its retardation effect on recrystallization and grain growth. In this work, dilute Al–0.07Sc and Al–0.07Sc–0.09Zr alloys were assessed with respect to the hot deformation and the post-brazing grain structure and compared with the base 1xxx alloy. The flow curves of the hot compression tests showed that the Al–Sc–Zr alloys exhibited higher flow stresses compared to the base alloy. The microstructure of the deformed samples in all three investigated alloys exhibited a recovered microstructure, but both Sc-containing alloys showed an improvement in the resistance to dynamic recovery. EBSD maps after a high temperature simulated brazing showed that the microstructure of the base alloy suffered from abnormal grain growth. Severe grain coarsening was still observed in the recrystallized microstructure of Al–0.07Sc alloy after brazing. The combined addition of Sc and Zr in Al–0.07Sc–0.09Zr alloy suppressed the abnormal grain growth, showing an improved control on the brazed microstructure. After post-braze aging at 350 °C for 4 h, the hardness of both Sc-containing alloys increased by 90–122% relative to the base alloy hardness.


Effect of Sc and Zr Microalloying on Grain Structure After Hot Deformation and Brazing in Al–Mn 3xxx Alloys

February 2024

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23 Reads

Al–Mn 3xxx alloys are widely used in the fabrication of multi-port extruded (MPE) tubes for aluminum heat exchangers. The industrial manufacture for those tubes consists of four steps: (1) homogenization, (2) extrusion, (3) straightening/sizing, and (4) brazing. The combination of cold work and brazing could result in abnormally coarsened grains that have negative impacts on the in-service performance of MPE tubes. A 3xxx alloy microalloyed with 0.08 wt.% Sc and 0.09 wt.% Zr was assessed with respect to the grain structures after hot deformation and brazing, and a comparison was made with the base 3xxx alloy free of Sc and Zr. The flow stress of the base alloy during hot compression at 500 °C and 1 s−1 was 48 MPa, while the alloy with added Sc and Zr showed a higher flow stress of 61.5 MPa. EBSD maps after hot deformation showed that the alloy with added Sc and Zr exhibited more resistance to dynamic recovery and dynamic recrystallization. After the high-temperature simulated brazing at 605 °C, the base alloy suffered from abnormal grain growth, whereas the alloy with added Sc and Zr exhibited an elongated recrystallized microstructure with a finer grain size.


Effect of Sc and Zr Additions on Dispersoid Microstructure and Mechanical Properties of Hot-Rolled AA5083

February 2023

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30 Reads

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2 Citations

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Paul Rometsch

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[...]

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X.-Grant Chen

5xxx5xxxaluminum alloysAluminum alloys are traditionally considered non-heat-treatable. With the addition of Sc/Zr and multistep heat treatmentHeat treatment, two kinds of dispersoidsDispersoids (AlMn and Al3(Sc,Zr)) were formed. The effect of Sc additions (0.08–0.43 wt.%) on dispersoidDispersoids formation and mechanical propertiesMechanical properties of hot-rolled sheets was investigated. The results showed that tensile properties initially increased with increasing Sc addition. The yield strength (YS) and ultimate tensile strengthTensile strength (UTS) of the alloy with 0.16 wt.% Sc reached 295 and 411 MPa, respectively, showing improvementsImprovement of 28% in YS and 8% in UTS compared to the base alloy. However, with a further increase of Sc, the tensile properties declined owing to the formation of a line/fan-shaped microstructureMicrostructure associated with discontinuous Al3(Sc,Zr) precipitationPrecipitation during solidificationSolidification. The evolution of Al3(Sc,Zr) and AlMn dispersoidsDispersoids during heat treatmentHeat treatment and hot rollingHot rolling was characterized using scanning and transmissionTransmission electron microscopies. Their influence on the mechanical propertiesMechanical properties of hot-rolled AA5083 alloys was discussed.


Use of Sc to Improve the Properties of AA5083 Cast and Rolled Products

February 2023

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45 Reads

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2 Citations

The properties of 5xxx5xxxaluminum alloysAluminum alloys can be improved with small additions of Sc. When Sc and Zr are added to 5xxx alloys, the alloys become heat-treatable as Al3(Sc,Zr) nanoprecipitates form at 300–400 °C. However, the heat treatmentHeat treatment and thermo-mechanical processingProcessing (TMP) need to be adapted to maximize the value of the Sc addition. In this work, AA5083 slabs were DC cast with and without minor additions of Sc and/or Zr. The room/elevated temperature mechanical propertiesMechanical properties of the cast materials were evaluated after various annealingAnnealing and homogenizationHomogenization treatments. Samples were then hot and cold rolled with different TMP treatments. The microstructureMicrostructure, room temperature mechanical propertiesMechanical properties and corrosionCorrosion performance were evaluated for selected tempers. It was evident that the properties could be improved significantly with small additions of Sc, but that this depends very much on the amount of Sc and on the processingProcessing parameters.


Effects of AlMn dispersoids and Al3(Sc,Zr) precipitates on the microstructure and ambient/elevated-temperature mechanical properties of hot-rolled AA5083 alloys

September 2022

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136 Reads

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22 Citations

Materials Science and Engineering A

With the addition of Sc and Zr to AA5083 alloy, two populations of strengthening particles (submicron-sized AlMn dispersoids and nanosized Al3(Sc,Zr) precipitates) precipitate during three-step heat treatment. Here, their influence on the microstructure and mechanical properties of hot-rolled sheets at ambient and elevated temperatures was investigated. The results show that the low-temperature (25–200 °C) tensile properties of the rolled sheets were significantly improved by increasing the Sc and Zr contents. The yield strength (YS) and ultimate tensile strength (UTS) of the alloy with 0.16 wt.% Sc and 0.17 wt.% Zr at ambient temperature reached 295 and 411 MPa, respectively, showing improvements of 30% in YS and 11.8% in UTS compared to the base alloy. However, the YS of the Sc/Zr-containing alloys at high temperature (300–400 °C) were lower than that of the base alloy. The mechanical properties of both the base and Sc/Zr-containing alloys were thermally stable during long-term thermal exposure at 300 °C for 500 h, demonstrating the great potential of this alloy for various elevated-temperature applications. The characteristics of the AlMn dispersoids and Al3(Sc,Zr) precipitates after the heat treatment and hot rolling were examined and quantified using transmission electron microscopy. Their combined contributions toward the YS at 25 and 300 °C were analyzed with the aid of constitutive strengthening equations and compared with experimentally measured values.


Citations (22)


... Conventionally, Al-Mg alloys are classified as non-heat-treatable and can only be reinforced through solid solution strengthening and work hardening [3][4][5][6], thus the attainable strength of these alloys is inherently lower than that of heattreatable aluminum alloys, limiting their further applications. It was been found that the co-addition of Sc and Zr forms Al 3 (Sc, Zr) dispersoids with a core-shell structure [7,8], significantly improving the mechanical properties [9][10][11][12] and thermal coarsening resistance [13,14] of the alloys. The formation of core-shell Al 2 (Sc, Zr) dispersoids with L1₂ structure minimizes the lattice mismatch with the α-Al matrix, resulting in a strong coherent interface [15]. ...

Reference:

The dispersoid evolution, recrystallization and mechanical properties of an Al–Mg–Sc alloy under various homogenization and annealing processes
Impact of hot rolling temperature on the mechanical properties and microstructural evolution of hot/cold-rolled AA5083 with Sc and Zr microalloying
  • Citing Article
  • March 2024

Material Science and Engineering

... Our previous studies [10,19] found that adding 0.08% Sc moderately improved the mechanical properties of AA5083 hot-rolled sheets, whereas the addition of 0.15% Sc significantly increased the tensile properties owing to the precipitation of an increased number density of L1 2 -Al 3 (Sc,Zr) nanoparticles. However, further increasing the Sc to 0.43% decreased the tensile properties, mainly because of the negative effect of discontinuous precipitation of L1 2 -Al 3 (Sc,Zr) [25,26]. ...

Effect of Sc and Zr Additions on Dispersoid Microstructure and Mechanical Properties of Hot-Rolled AA5083
  • Citing Chapter
  • February 2023

... Some annealed samples were further cold-rolled to 0.85 mm thickness, representing a 15% reduction (near H116-temper). A part of the annealed sheet samples was cold-rolled from 1 mm to 0.8 mm (20% reduction) and stabilized at 185 °C/1 h followed by air cooling (near H321-temper) [43]. ...

Use of Sc to Improve the Properties of AA5083 Cast and Rolled Products
  • Citing Chapter
  • February 2023

... Algendy et al. [22] found that as three-step homogenization (430 °C/2 h + 480 °C/2 h + 525 °C/2 h) can efficiently dissolve low-melting-point eutectic phases, however, the Al 3 (Sc, Zr) dispersoids are coarsened, resulting in lower strengthening effect. Later, a new three-step homogenization is developed by the same author [23], in which the initial two steps (275 °C/12 h + 375 °C/48 h) can maximize the precipitation of AlMn and Al 3 (Sc, Zr) dispersoids, while the third step (425 °C for 12 h) ensures complete dissolution of low-melting eutectic phases while minimizing dispersoid coarsening. Nevertheless, the impact of single-stage versus multi-stage homogenization on alloy performance remains insufficiently understood. ...

Effects of AlMn dispersoids and Al3(Sc,Zr) precipitates on the microstructure and ambient/elevated-temperature mechanical properties of hot-rolled AA5083 alloys
  • Citing Article
  • September 2022

Materials Science and Engineering A

... Conventionally, Al-Mg alloys are classified as non-heat-treatable and can only be reinforced through solid solution strengthening and work hardening [3][4][5][6], thus the attainable strength of these alloys is inherently lower than that of heattreatable aluminum alloys, limiting their further applications. It was been found that the co-addition of Sc and Zr forms Al 3 (Sc, Zr) dispersoids with a core-shell structure [7,8], significantly improving the mechanical properties [9][10][11][12] and thermal coarsening resistance [13,14] of the alloys. The formation of core-shell Al 2 (Sc, Zr) dispersoids with L1₂ structure minimizes the lattice mismatch with the α-Al matrix, resulting in a strong coherent interface [15]. ...

Evolution of discontinuous/continuous Al3(Sc,Zr) precipitation in Al-Mg-Mn 5083 alloy during thermomechanical process and its impact on tensile properties
  • Citing Article
  • August 2022

Materials Characterization

... From the Ashby diagrams, tables, and figures that compile the properties and Merit Indexes of the alloys in question, in the case study of the wings spars, it can be inferred that the alloy of the Al-Mg-Sc system AA5028-H116 which was Additively Manufactured by Laser Powder Bed Fusion [35][36][37][38] or Melt-Spinning [39,40] process, compared to AA alloy 7075-T6, has 0.52% higher mechanical strength limit, 5% higher yield strength limit, fracture toughness 45.83% higher in TL orientation and 29.6% higher in LT orientation, equivalent elongation, equivalent Brinel hardness, and 166.7% higher fatigue strength limit. Thus, consequently, when analyzing the Merit Indexes table, it can be seen that the Al-Mg-Sc system alloy AA5028-H116 has the highest index E 1/2 /ρ equal to 3.19, and the highest index δy 2/3 /ρ equal to 25.313, which shows the superiority of AA5028-H116 compared to the remaining alloys in the classification concerning the mechanical properties involved in them. ...

Review of High-Strength Aluminium Alloys for Additive Manufacturing by Laser Powder Bed Fusion
  • Citing Article
  • May 2022

Materials & Design

... During structure build-up, elevated temperature may activate diffusion processes; however, local temperature and holding time are indirectly influenced, e.g. the first layers may be held at an elevated temperature for relatively longer than the final layers due to prolonged heat input from the AM process. Achieving homogeneous peak ageing requires strict control over temperature and holding time, which cannot currently be achieved during AM, thus leading to undesirable precipitation and hardness gradients in the AM structure [35,36]. Although hardness cannot be directly correlated with mechanical properties such as tensile strength and ductility, areas with high hardness generally exhibit higher strength than areas with low hardness [37,38]. ...

Production Strategy for Manufacturing Large-Scale AlSi10Mg Components by Laser Powder Bed Fusion
  • Citing Article
  • January 2021

JOM: the journal of the Minerals, Metals & Materials Society

... The primary strengthening mechanism is provided by the formation of precipitation of 2 , which significantly depends on temperature. However, since the precipitate is highly sensitive to the high-temperature environment (Temperature > 200°C), a significant drop in mechanical strength was observed in the welded specimens [22][23][24][25]. By introducing a filler metal (AA 4043), a large amount of silicon is available to form the precipitate. ...

Improving the Mechanical Response of Al-Mg-Si 6082 Structural Alloys during High-Temperature Exposure through Dispersoid Strengthening

Materials

... The energy consumption and carbon emissions are only 5% of that of electrolytic aluminum [9,10], but will introduce many Fe elements. This iron forms coarse intermetallic compounds with Al, Si, and other components, which affect the microstructure and properties of Al-Si-Mg alloy [11][12][13][14]. Due to the presence of a significant number of impurity Fe elements, Al-Si alloys can form various Fe-rich intermetallic compounds during solidification, including which precipitate before primary α-Al and then distribute in the dendrites. ...

Effects of Al(MnFe)Si dispersoids with different sizes and number densities on microstructure and ambient/elevated-temperature mechanical properties of extruded Al-Mg-Si AA6082 alloys with varying Mn content
  • Citing Article
  • November 2020

Journal of Alloys and Compounds

... The fine equiaxed grains formed at the melt pool boundaries, whereas the columnar ones formed within the melt pools. The precipitation of Al 3 (Sc,Zr) promoted nucleation of α-Al grains, resulting in a refined α-Al grain structure, particularly at the melt pool boundaries due to a faster solidification rate [32,33]. ...

Precipitation kinetics, microstructure evolution and mechanical behavior of a developed Al-Mn-Sc alloy fabricated by selective laser melting
  • Citing Article
  • May 2020

Acta Materialia