Zn-free Alloy Research Articles

Structure Evolution and Mechanical Properties of Sheet Al–2Cu–1.5Mn–1Mg–1Zn (wt.%) Alloy Designed for Al20Cu2Mn3 Disperoids

This work was focused on studying the possibility of increasing the strength of non-heat-treatable sheet alloy Al2Cu1.5Mn (wt.%) by the joint addition of 1% Mg and 1% Zn. The effect of these elements on the structure and mechanical properties of the new sheet Al2Cu1.5Mn alloy designed for Al20Cu2Mn3 dispersoids has been studied by calculations and experimental methods. The obtained data on the phase composition, microstructure, and physical and mechanical properties of the new alloy for different processing routes (including hot rolling, cold rolling, and annealing) have been compared with those for the ternary Mg- and Zn-free alloy. It has been shown that the formation of nanosized Al20Cu2Mn3 dispersoids (~7 vol.%) provides for the preservation of the non-recrystallized grain structure after annealing at up to 400 °C (3 h), while Mg and Zn have a positive effect on the strength due to the formation of alloyed aluminum solid solution. As a result, cold-rolled sheets of the Al2Cu1.5Mn1Mg1Zn model alloy showed a substantially higher strength performance after annealing at 400 °C in comparison with the ternary reference alloy. In particular, the UTS is ~360 vs. ~300 MPa, and the YS is 280 vs. 230 MPa. For the example of the Al2Cu1.5Mn1Mg1Zn model alloy, it has been shown that the system is promising for designing new heat-resistant alloys as a sustainable alternative to the 2xxx alloys. The new alloy has an advantage over the commercial alloys (particularly, 2219, 2024, 2014), not only in manufacturability but also in thermal stability. The sheet production cycle for the model alloy is much shorter because the stages of homogenization, solution treatment, and water quenching are excluded.

Effect of trace Zn addition on microstructure and corrosion behavior of AA2024 under different aging treatments

The effect of trace Zn (0.67 wt%) addition on the microstructure and corrosion behavior of AA2024 under different aging treatments was investigated. The results reveal that, with trace Zn addition, the corrosion depth decreases at the natural aging condition, but increases at the artificial aging treatment (both the peak aging condition and over aging condition). The corrosion morphology of the Zn-containing alloy under different aging treatments is also different from that of the Zn-free alloy. Compared with the Zn-free alloy, the dealloying process of the S phase in the Zn-containing alloy is slower, which are not conducive to the formation of pitting corrosion. Transmission electron microscope shows that trace Zn addition can promote the nucleation of the intragranular Guinier-Preston-Bagaryatski zones which transform into S phases in the subsequent aging process. Compared with the Zn-free alloy, the S phases of the Zn-containing alloy are coarser at the over aging condition. Moreover, details of how the corrosion morphology of Zn-containing alloys changed and the relationship between the microstructure and the corrosion behavior were discussed. • Trace Zn inhibits the dealloying of Intermetallic S particles. • The local corrosion depth at the natural aging condition is small and the local corrosion depth at the artificial aging condition is large in the AA2024 with trace Zn compared with the Zn free alloy. • Zn segregated at the S-Al interface has been characterized. • Trace Zn promotes the growth and coarsening of grain boundary S phase particles in the AA2024 under artificial aging treatments. • Zn promotes the coarsening of S phase at the grain boundary and the aggregation of Zn at the S-Al interface works together on the local corrosion morphology of the alloy.

Development of high strength sand cast Mg–Gd–Zn alloy by co-precipitation of the prismatic β′ and β1 phases

In order to design a high strength sand cast Mg–Gd–Zn alloy, the microstructures and mechanical properties of cast Mg–12Gd–xZn–0.4Zr (x = 0, 0.4, 0.8) (wt%, signed as GZ1200K, GZ1204K and GZ1208K) alloys were studied. Zn addition changes the constitution of the strengthening phases in Mg12Gd alloy. Small amount of Zn addition leads to the formation of basal precipitates of γ″ and γ′, accelerated-precipitation of the β1 phases and lower number density of the prismatic β′ phases, and modifies the morphology of the prismatic β′ precipitates. Compared with the Zn-free alloy, the Zn-containing alloys (GZ1204K & GZ1208K) having higher yield strength in peak-aged and over-aged conditions are mainly due to the extra prismatic β1 precipitates, which do not precipitate in the Zn-free alloy. Under sand casting condition, GZ1208K alloy strengthened by the co-precipitates of the prismatic β′ and β1 phase indicates a good combination of strength and ductility at room temperature: yield strength of 270 MPa, ultimate tensile strength of 348 MPa and elongation of 2.6%.

Precipitation modification in cast Mg–1Nd–1Ce–Zr alloy by Zn addition

Abstract The effects of different Zn addition (0, 0.2, 0.5, 1.0 wt%) on the microstructure and mechanical properties of cast Mg–1Nd–1Ce–Zr alloy in as-cast, solution-treated and 200 °C peak-aged conditions were studied. Precipitates in cast Mg–1Nd–1Ce–Zr alloy are significantly modified by the Zn addition. In the Zn-free alloy, the disk-shaped prismatic precipitates and the point-like precipitates are the main strengthening phases. When 0.2 Zn is added, the disk-shaped precipitates are refined and very fine basal precipitates form additionally. When 0.5 Zn is added, the basal precipitates become the main strengthening phase. Further increasing the Zn addition to 1.0%, only spare basal precipitates and point-like precipitates exist. The 0.5 Zn addition alloy has the highest strength at room temperature, whose yield strength, ultimate tensile strength and elongation in T6 condition are 136 MPa, 237 MPa and 9%, respectively.

Achieving enhanced mechanical properties in Mg-Y-Sm-Zr alloy by altering precipitation behaviors through Zn addition

The effects of 0.5 wt% Zn addition on microstructural evolution and mechanical properties in Mg-7Y-5Sm-0.3Zr alloy were investigated. The results showed that after solution treatment, LPSO phase precipitated only at grain boundaries in Zn-containing alloy, while RE-containing cuboid compound appeared in both alloys (Zn-free and Zn-containing). A large number of Mg5(Y,Sm) precipitated dynamically during hot extrusion in Zn-free alloy, while there was only a few Mg5(Y,Sm) in Zn-containing alloy after hot extrusion. Furthermore, many basal γ′ precipitates and lamellar LPSO were observed in grain interior in extruded 0.5Zn alloy. In subsequent aging process, the two alloys exhibited the same peak-aged Vicker hardness and identical precipitates (β'). The extruded 0.5Zn alloy after peak-aging treatment exhibited a yield strength (YS) of 413 MPa and an ultimate tensile strength (UTS) of 465 MPa with an elongation to failure (EL) of 6.5%, which were 370 MPa, 413 MPa and 5.8% respectively, for the 0Zn alloy. The strength improvement after Zn addition is mainly attributed to the synergistic contribution of LPSO structure, γ′ precipitates and β' phase.

Natural aging behavior in pre-aged Al–Mg–Si–Cu alloys with and without Zn addition

This study investigates the clustering behavior and its correlation with the change in hardness during natural aging (NA) after pre-aging (PA) at 80 °C for 15 min in Al–Mg–Si–Cu alloys with and without Zn addition. The results show that NA after PA causes the growth of clusters in the Zn-free and Zn-added alloys, which is related to the partitioning of solute atoms from the Al matrix into clusters. Si exhibits considerably stronger partitioning than Mg during NA after PA, which leads to an increase in the number of Si-rich clusters. Cu can also be partitioned into clusters of two alloys when the NA after PA is conducted. Zn is present in the clusters of the Zn-added alloy during NA after PA. The addition of Zn increases the growth rate of clusters. In addition, the increased volume fraction of clusters explains the increased hardness of the Zn-free and Zn-added alloys during NA after PA. Compared with the Zn-free alloy, the Zn-added alloy exhibits a more significant change in volume fraction of clusters, thus achieving an enhanced age hardening response.

The roles of long period stacking ordered structure and Zn solute in the hot deformation behavior of Mg-Gd-Zn alloys

In order to investigate the roles of long period stacking ordered (LPSO) structure and Zn solute in the hot deformation behavior of Mg-Gd-Zn alloys, the Mg-12Gd-1Zn-1Mn-0.5Zr alloy containing LPSO phase or Zn solute was hot compressed under various deformation conditions in comparison with the Zn-free Mg-12Gd-1Mn-0.5Zr alloy. The results showed that the Zn-containing alloys had stronger softening effects, larger peak stress and higher average activation energy than the Zn-free one within the safe deformation domain. Both LPSO phase and Zn solute in α-Mg matrix increased the efficiency of power dissipation, narrowed down the flow stability regions of processing map and impeded the dynamic recrystallization (DRX), especially when Zn solute was mainly in α-Mg matrix. Furthermore, the LPSO phase or Zn solute in α-Mg matrix promoted the dynamic precipitation. A few Mg5Gd particles can be observed in the Zn-free alloy, while a large number of stacking faults (SFs) and LPSO phase were precipitated in the Zn-containing alloys, and they were eventually transformed into Mg5Gd particles at low strain rate.

Precipitation hardening behavior and microstructure evolution of Al–5.1 Mg–0.15Cu alloy with 3.0Zn (wt%) addition

The precipitation hardening behavior of Al–5.1Mg–0.15Cu alloy with 3.0Zn (wt%) addition at various temperatures has been systematically investigated in this study. The Al–5.1Mg–0.15Cu–3.0Zn alloy possesses the higher strength compared with traditional Zn-free alloy, when the alloy is treated at 363 K for 24 h and subsequently aged at 413 K for 25 h. The precipitation sequence of the hardening phase T-Mg32(AlZn)49 is investigated by differential scanning calorimetry tests, transmission electron microscopy and high-resolution electron microscopy. The different effects of natural aging and pre-aging on the precipitation hardening behavior are detailed. The formation of relatively stable Guinier–Preston zones of T-Mg32(AlZn)49 phase during pre-aging rather than natural aging results in higher mechanical strength during subsequent artificial aging at relatively high temperatures. When the Al–5.1Mg–0.15Cu–3.0Zn alloy is aged at 453 K, the peak hardness is from synergetic effect of hardening of S-Al2CuMg phase and coarsening of T phase. However, during two-step artificial aging treatment, the peak hardness results from fine, spherical and homogeneously distributed T phase in the absence of the S phase.

Effect of Zn addition on the precipitation behaviors of Al–Mg–Si–Cu alloys for automotive applications

Effect of Zn addition on the precipitation kinetics and age-hardening response of Al–Mg–Si–Cu alloys was investigated by differential scanning calorimetry (DSC), hardness measurements, tensile tests and microstructural characterization. The results show that, compared with the Zn-free alloy, both the starting and peak temperatures in the DSC curve, and activation energy of β″ precipitation of Zn-added Al–Mg–Si–Cu alloy decrease significantly, corresponding to the greatly improved precipitation kinetics and age-hardening response, i.e., a hardness increment of 70HV after aging at 185 °C for 20 min. Moreover, the peak hardness and tensile properties can also be greatly enhanced after adding 3.0 wt% Zn even exhibiting a ductile fracture feature in the peak-aged state. No precipitates of the Al–Zn–Mg alloy system appear in the Zn-added Al–Mg–Si–Cu alloys after aging at 185 °C, and pre-β″, β″, and L precipitates are still the main precipitates in the two alloys after peak aging treatment. Finally, based on the microstructural evolution, a schematic diagram of precipitation in the Al–Mg–Si–Cu–Zn alloy is put forward, and the relationship between mechanical properties and microstructure is also established.

Effect of Zn addition on the microstructure, texture evolution and mechanical properties of Al-Mg-Si-Cu alloys

Effect of Zn addition on the microstructure, texture evolution and mechanical properties of Al-Mg-Si-Cu alloys was investigated by mechanical properties, microstructure and texture characterization in the present study. The results show that Zn addition has a significant influence on the evolution of microstructure and texture, and final mechanical properties. Yield strength, ultimate tensile strength and elongation increase and average Lankford coefficient r value decreases with increasing Zn content. Although the microstructure evolution in both the Zn-free and high Zn-added alloy sheets during thermomechanical processing is basically similar to each other, both the different precipitate distribution in the annealing or rolling state, and recrystallization microstructure in the solution state still can be found. Additionally, Zn addition basically does not change texture component but decrease the intensity before solution treatment. However, Zn addition has a notable effect on the recrystallization texture evolution during solution treatment. The Zn-free alloy sheet is comprised of CubeND, P and Goss orientations, while the alloy sheet with high Zn content has stronger texture consisting of CubeND, Cube, {012}<100>, {113}<392> and {023}<032> orientations. Finally, effect of texture on r value was analyzed by Visco-plastic self-consistent (VPSC) model.

Effect of zinc additions on the microstructure mechanical properties and creep behavior of as-cast Mg–3Sm–0.4Zr (wt.%) alloy

The influence of zinc (Zn) additions (0, 0.5, 1wt.%) on the microstructure, mechanical properties of as-cast Mg–3Sm–0.4Zr (wt.%) alloy has been investigated in the present study. Compared with the Zn-free alloy, addition of 0.5wt.% Zn results in the formation of great amounts of fine precipitates in the regions close to grain boundaries, which effectively retard dislocation motion and dramatically enhance the tensile strength at 200 and creep resistance. For the alloy containing higher zinc content (=1wt.%), the excellent creep resistance is mainly attributed to the suppression of non-basal dislocation slip due to the presence of planar defects.

Influence of Zn Addition on Aging Response and Corrosion Resistance of Mg-Gd-Nd-Zr Alloy

The age hardening response and corrosion resistance of Mg-8%Gd-2%Nd-0.3%Zr alloys with various Zn contents up to 2% (in weight) have been investigated. The Zn-free alloy exhibits relatively lower age hardening and slower age response, whereas the addition of Zn enhances the age hardening response remarkably. The weight loss after salt spray test decreases with increasing Zn content in the peak-aged alloys, which is presumably associated with the increased amount of eutectic Mg-Zn-Nd-Gd phase acting as a corrosion barrier along the a grain boundaries. increases.

Enhanced age hardening response and creep resistance of Mg–Gd alloys containing Zn

Abstract Mg–6Gd–0.6Zr (wt.%) alloy exhibits little age hardening during isothermal ageing treatments and has low creep strengths. Additions of 1–2 wt.% Zn to this alloy significantly enhance the age hardening response and the creep strength. The remarkable improvement in strength and creep resistance is associated with a uniform and dense distribution of basal precipitate plates that are not observed in the Zn-free alloy.

Precipitation sequence in an Al-Cu-Mg-Ag-Zn alloy

Abstract The precipitation sequence at 190°C in a complex A1-4Cu-0·35Mg-0·7Ag-1·2Zn foundry alloy belonging to the commercial AVIOR composition has been investigated by means of differential scanning calorimetry and transmission electron microscopy, and a comparison with a Zn-free alloy has been made in order to evaluate the influence of Zn on the precipitation sequence. It is found that Zn modifies the sequence generally found in AlCuMgAg alloys having a high Cu: Mg ratio. The Ω′ precursor of the Ω-CuAl2 phase found in the Zn-free alloy is in fact not detectable and a different mechanism for Ω nucleation must be invoked. An active role of early θ″ and θ′ precipitates is proposed as precursors of Ω. It is also found that the presence of Zn strongly influences the kinetics of Ω precipitation, which is promoted at the expense of the θ′-CuAl2 and S'-CuMgAl2 phases. Well-assessed Ω particles are present after 15 min of ageing at 190°C, and in relevant amounts after 600 min, while only few θ′ precipitates and rare S′ particles heterogeneously nucleated on defects and homogeneously precipitated inside the grains can be found. The differences detected in the Zn-additioned alloy are interpreted in terms of reduction of the stacking fault energy obtained by the Zn alloying.

Mechanism of ?1 formation in conventional dental amalgams

This study reexamined the mechanism of β1 formation in conventional dental amalgams in the light of a previously unrecognized intergranular structure, the SnHg-δ2 phase. Two amalgams, A (45. 5% Hg) and B (65. 0% Hg), were made from a Zn-free alloy of the following composition (wt%): Ag-70, Sn-26, Cu-4. After storage at 37°C for 1 day, both amalgams were heat treated at 70°C for up to 16 days. The structural changes in the two amalgams as a function of their heat treatment were characterized by differential scanning calorimetry and X-ray diffraction techniques. On the basis of the experimental data, we have proposed a new mechanism on β1 formation. This mechanism involves a series of interrelated reactions. The primary one is a reaction between AgSn-γ and δ2 that leads to the nucleation of β1 at γ boundaries. Simultaneous operation of several secondary and tertiary reactions result in (1) further growth of β1 and its continuing change in composition, (2) loss of Sn from the δ1 matrix, (3) conversion of CuHg into η, and (4) a possible transformation of δ2 into Sn-rich β1 or α1.

New Pb-free solder alloy with superior mechanical properties

New high-strength Pb-free solder alloys, based on the Sn-Ag-Zn system, have been developed. A relatively small addition of Zn significantly improves the mechanical strength of Sn-3.5% Ag eutectic solders while maintaining the same level of ductility. The observed increase in strength is as much as 48% over that of the Zn-free alloy. This strengthening from the Zn additions is attributed to a substantial refinement of the precipitates in the solidification microstructure. The problems of nonuniformity in solidification dendrite structure and solder surface roughness often observed in the Sn-Ag binary alloys are also alleviated by the Zn addition. It is found that essentially all of the added Zn resides in the more corrosion-resistant, Ag-based, intermetallic precipitates, leaving the Sn-rich matrix primarily free of Zn in solid solution. High-temperature creep tests indicate that the new Zn-containing alloys exhibit a remarkably improved creep resistance of more than an order of magnitude.