Lightweight alloys in the automotive industry Advanced material

Lightweight alloys in the automotive industry Advanced material and technologies, MSc 2017 1

Types of lightweight alloys Non prec. hardenable Prec. hardenable Wrought For casting 2

Example for precipitation process from supersaturated solid solution • Precipitation hardening in Al-based alloys: in this case precipitation in more than one step! Curiosity: Al-brass (Cu alloys with Al) have same phenomenon as at steels → martensitic like transformations, after quenching high hardness and low inpact energy. 3

What are all made of Mg-based alloys? Engine block made of Al-Mg alloy 4

It is used not only in automotive industry Components are made of Mg alloys 5

Mg production and distribution capacity across the world 6

The most important properties of Mg General properties Atomic number 12 Period alkaline earth metal Group, period, block 2, 3, s Atomic mass 24, 305 g/mol Magnetism paramagnetic Physical properties State of matter (at room temp. ) solid Density ρ=1, 738 g/cm 3 Young modulus E = 45 Gpa Melting point 650°C (923 K ) Boiling point 1090°C (1363 K) Enthalpy of melting 8, 48 k. J/mol Enthalpy of vaporization 128 k. J/mol Heat of combustion 25, 2 MJ/kg Atomic properties Type of lattice hexagonal 1 : 737, 7 k. J//mol Ionization energies (1, 2, 3) 2 : 1450, 7 k. J/mol 3 : 7732, 7 k. J/mol 7

Alloying elements Mg alloys with limited solid solubility: In every cases precipitation processes are involved (either melt or solid state: secondary processes). 8

Commonly used alloying elements Char. Alloying Char. Alloying A Aluminium M Manganese C Copper Q Silver E Rare earth metals S Silicon H Thorium W Yttrium J Strontium X Calcium K Zirconium Z Zinc L Lithium Al AZ 91 D (ASTM) MGAl 9 Zn 1 D (MSZ EN) 8, 5 -9, 5 Mn 0, 17 -0, 4 Zn Si Cu Ni Fe 0, 45 -0, 9 0, 05 0, 025 0, 001 0, 004 9

The most common alloy as a structural material 10

Eutectics have a key role in the design of structural Mg alloys 11

Role of primer crystallisation and precipitation processes Mg-Alsss: Mg(Al) supersaturated solid solution 12

Introduction Magnesium-based hybrid materials are applied in engine componenets. Because of construction these materials with different machinability have to be cut together. During simultaneous machining the cutting edge intersects the boundary of the jointed materials. Source: EMO (2005) Source: mwerks. com (2003) 13

Introduction The BMW Mg-Al crankcase Source: mwerks. com (2003) The BMW Mg-Sint bedplate Source: mwerks. com (2003) 14

Introduction AIM: Economical and ecological simultaneous milling of Mg+sintered steel hybrid materials. Challanges of dry machining of Mg-SD hybrid material: Different cutting forces Different cutting temperatures Mg chip and dust → Fire hazard Different cutting edge geometries Different cutting parameter (speed) Mg: bottom limit SD 11: upper limit Optimized cutting edge material geometry Temperature control during machining Machine with safety concept 15

Characterization of Mg-hybrid boundary (Result of previous tool optimization experiments, presented on 24 th Colloquium in Svitavy. ) 16

In addition to the known advantageous properties of Mg: increased fire risk! Where does an emergency occur? - manufacturing, machining, - fire at vehicle accidents. 17

Fontosabb technológiai ismeretek a Mg-tűz megelőzésére • • A bomlás során magnézium oxid (Mg. O) nagy mennyiségű hidrogén gáz, valamint további nagy mennyiségű hő fejlődik. 1. ábra Mg reakciója gőzzel • Ennél a reakciónál szükségszerű megemlíteni, hogy ha nagyon tiszta tömbi magnéziumot reagáltatunk vízzel, akkor az viszonylag csekély mértékben és csak rövid ideig mutat reakciót. Ennek oka a következő reakció egyenletben keresendő. • • 2. ábra Tiszta tömbi magnézium reakciója vízzel Ebben az esetben magnézium oxid helyett magnézium hidroxid keletkezik, ami egy tejszerű oldhatatlan folyadék 18

A tűz keletkezése az alkatrész tömegétől, geometriájától, a hőmérsékletétől függ 19

Common production (casting, shaping) technologies for Mg based alloys Forrás: E. J. Vinarcik, High Integrity Die Casting Processes, John Wiley & Sons, Inc. , New York, 2003 20

Special production technologies for Mg based alloys There are many reasons for introducing special molding and shaping technologies: - the increased work safety problems, - economic goals - as a structural material we should increase the strenght (precipitation hardening, work hardening and combination of these) 21

The phenomenon of creep l = const. T= const. rupture t. R lg t 22

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What kind of mechanisms lead to strength enhance? 24

The technologies applied here already in the field of composite manufacturing technology 25

Thixo-forming Definition: Thixotropy For metals at a temperature between the solidus and the liquidus, liquid phase exists in addition to the solid, coherent particles. At this time, in a resting state, the material behaves as a solid body. When a shear stress is applied to this mixed phase material, the bonds between the particles are broken, the viscosity decreases considerably and the metal acts as a high viscosity fluid. This property is thixotropy. Thixotropy is formed in a temperature range well defined for certain metals, especially aluminium and magnesium alloys. Thixotropy in general: (Bauer and Collins) if the rheological properties of a system (elasticity modulus, yield strength, viscosity) have a reversible change due to shearing stress and at constant temperature, and the recovery time depends on the value of the applied stress, the system is thixotropic. 26

Thixo-forming The process of thixo-forming (1): 1. Production of semi-finished product (eg. molded bars): Purpose: fine grain structure. (For example, controlling crystal formation with electromagnetic fields. ) 2. Reheating of semi-finished products: The base material is heated up between the liquidus and the solidus. This heating creates the fully globulite (spherical) structure from the fine-grained structure, which is most advantageous in terms of shaping. The liquid phase distribution must be balanced and the temperature gradient must be minimum. 27

Thixo-forming The process of thixo-forming (2): 3. Forming: The semi-finished products are placed in a container of a casting machine developed for the needs of thixo shaping. When flowing from the container to the nozzle, due to the significant cross-sectional reduction, shear stress is awakened in the material. As a result of the shear stress, the bonds between the spherical particles are torn off and become a high viscosity liquid in the full volume of the material. This is the phenomenon of thixotropy. After the shear stress is reduced, the viscosity increases with its original value only with significant delay. As a result of the compression force, liquid metal fills the preheated mold with laminar flow. 4. Post-machining 28

Thixo-forming Dendritic structure Globulitic structure 29

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Thixo-forming / Die-casting Thixo-forming with laminar flow of the melt Die-casting with turbulent flow of the melt 31

2 nd Consortium meeting M 1 25 -26 th of November, 2004 Barcelona 1. Workpiece materials 1. AJ 62 + Al. Si 17 cylinder block upper and lower surface 2. AJ 62 + sintered steel lower cranckshaft bearing casing – “bed plate” Figure 2 – Scheme of engine block to be machined 32 Budapest University of Technology and Economics Department of Vehicles Manufacturing and Repairing