Continuous galvanizing of martensitic and complex phase steels for automotive anti-intrusion applications

From the perspective of crashworthiness andpassenger safety, martensitic and complexphase Ultra High Strength Steels (UHSS) areideal candidates for automotive anti-intrusioncomponents. However, these steels must beprotected from corrosive environments in orderto maintain the longterm integrity of thestructures involved for which continuousgalvanizing is a cost-effective solution. Severalchallenges have to be overcome in order toprocess the above steels in the continuousgalvanizing line (CGL) while achieving theminimum target tensile strength of 1250 MPa.Steel chemical compositions should be selectedin such a way that maintaining a suitablecooling rate produces martensite or bainite,and also provides a substrate surface withsufficient reactive wetting suitable forgalvanizing. In the present study, steelchemistries were designed around relativelylean compositions based on carbon,manganese and silicon with additionalhardenability being provided by molybdenumor chromium additions. Annealing cycles weredetermined based on the continuous coolingtransformation behaviour of the steels. For bothsteel compositions the target tensile strength of1250 MPa was achieved using austeniticannealing for 120s followed by cooling to roomtemperature at 50°C/s. The steels weresuccessfully reactively wet by the Zn(Al,Fe) bathusing a 95%N2-5%H2, -30°C dew pointprocess atmosphere. From scanning electronmicroscopy, X-ray photoelectron spectroscopyand scanning Auger microscopy it wasdetermined that oxides of manganese, siliconand chromium formed during annealing.However, these oxides did not have an adverseeffect on coatability and both steels formed highquality, adherent coatings

Experimental study of the Al-Mg-Sr phase diagram at 400°C

TheAl-Mg-Sr systemis experimentally studied at 400∘C using EPMA and XRD techniques. It was determined that the intermetallic phases in the Al-Mg-Sr system have a tendency to form extended substitutional solid solutions. Two ternary phases were found in this system. Solubility limits of binary and ternary phases were determined and the phase equilibria among phases were established. The isothermal section of the Al-Mg-Sr system at 400∘C has been constructed using results of the phase analysis and experimental literature data

New Phases in the Mg-Al-Sr System

Abstract. This work presents experimental investigation of 14 different alloys with differential scanning calorimetery (DSC), scanning electron microscopy/energy dispersive spectrometer (SEM/EDS) analysis, quantitative electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) techniques to identify the phases in the Mg-Al-Sr system and to determine their compositions. DSC has permitted real time measurement of the phase changes involved in these systems. The temperature ranges for the phase transformations and enthalpy of melting and enthalpy of formation of the compounds are reported. Comparison between these results and the thermodynamic findings has been discussed. The microstructure of the Mg-Al-Sr-based alloys is primarily dominated by (Mg) and (Al 4 Sr). The plate-like structure has been identified as Al 4 Sr. A new ternary intermetallic with chemical composition of 69.9 ± 1.5 at.% magnesium, 19.3 ± 2.0 at.% aluminum and 8.7 ± 0.6 at.% strontium has been identified in three different alloys. This phase was characterized as a large precipitate. Three ternary solid solutions have been observed. The solubility ranges of Al in Mg 38 Sr 9 and Mg 17 Sr 2 are 12.5 and 8.5 at.%, respectively, whereas the solubility of Mg in Al 4 Sr compound is found to be 23 at.% in the investigated samples. Further, Mg was found to dissolve 11.4 at.% Al at room temperature

Properties of Galvanized and Galvannealed Advanced High Strength Hot Rolled Steels

The objectives of the project were (i) to develop the coating process information to achieve good quality coatings on 3 advanced high strength hot rolled steels while retaining target mechanical properties, (ii) to obtain precise knowledge of the behavior of these steels in the various forming operations and (iii) to establish accurate user property data in the coated conditions. Three steel substrates (HSLA, DP, TRIP) with compositions providing yield strengths in the range of 400-620 MPa were selected. Only HSLA steel was found to be suitable for galnaizing and galvannealing in the hot rolled condition

On the precipitates and mechanical properties of magnesium–yttrium sheets

Light-weight wrought magnesium alloys is an important part of the weight reduction in automobiles industry for improve their fuel efficiency. Yttrium containing magnesium alloy is a potential material in this perspective. In this work, two magnesium–yttrium alloys (C and D alloys) were cast and rolled to 2 mm thick sheets. The mechanical properties of these hot rolled and annealed sheets were determined. Optical microscope and scanning electron microscope equipped with EDX were used to investigate microstructure evolution during thermo-mechanical processing in the studied alloys. Precipitates evolution during hot rolling and annealing processes were analyzed and compared with those calculated using thermo-chemical software (FactSage). Schiel phase distribution diagrams of C and D alloys were calculated using FactSage

Superplasticity and microstructural stability in a Mg alloy processed by hot rolling and friction stir processing

The superplastic behavior of a Mg-1.2 Zn-1.7 Y-0.53 Al-0.27 Mn alloy sheet processed by hot rolling and friction stir processing (FSP) was investigated. The kinetics of superplastic deformation were compared with Mg-3 Al-1 Zn and other Mg-Zn-Y alloys processed by different methods. The FSP Mg-1.2 Zn-1.7 Y-0.53 Al-0.27 Mn alloy exhibits slower kinetics of deformation compared with other alloys. The microstructural stability of the FSP Mg-1.2 Zn-1.7 Y-0.53 Al-0.27 Mn alloy is better than the Mg-3 Al-1 Zn alloy because of the presence of different types of precipitates

Superplasticity and microstructural stability in a Mg alloy processed by hot rolling and friction stir processing

The superplastic behavior of a Mg-1.2 Zn-1.7 Y-0.53 Al-0.27 Mn alloy sheet processed by hot rolling and friction stir processing (FSP) was investigated. The kinetics of superplastic deformation were compared with Mg-3 Al-1 Zn and other Mg-Zn-Y alloys processed by different methods. The FSP Mg-1.2 Zn-1.7 Y-0.53 Al-0.27 Mn alloy exhibits slower kinetics of deformation compared with other alloys. The microstructural stability of the FSP Mg-1.2 Zn-1.7 Y-0.53 Al-0.27 Mn alloy is better than the Mg-3 Al-1 Zn alloy because of the presence of different types of precipitates