The paper presents research on the effects of soft annealing parameters on a change of the impact strength KC and Brinell hardness (HB)

of the EN AC-AlSi11 alloy. The research has been performed according to the trivalent testing plan for two input parameters –

temperature in the range between 280°C and 370°C and time in the range between 2 and 8 hours. The application of such heat treatment

improves the plasticity of the investigated alloy. The improvement of the impact strength KC by 71% and the decrease of the hardness HB

by 20% was achieved for the soft annealing treatment conducted at a temperature 370°C for 8 hours, compared to the alloy without the

heat treatment. A change of the form of eutectic silicon precipitations which underwent refinement, coagulation and partial rounding, had

a direct effect on the hardness HB and impact strength KC. The results obtained were used to prepare space plots enabling the temperature

and time for soft annealing treatment to be selected with reference to the obtained impact strength KC and hardness HB of the alloy with

the heat treatment.

The present work discusses results of increased temperature on shape-dimensional changes of a 110 type hose coupling, produced from EN AC-AlSi11 alloy with the use of pressure die casting technology. The castings were soaked for 3.5 h at temperatures 460°C, 475°C and 490°C. The verification of shape-dimensional accuracy of the elements after soaking treatment, in relation to raw casting, was carried out by comparing the 3D models received from 3D scanning. Soaking temperature of about 460°C-475°C results in no significant changes in the shapes and dimensions of the castings, or surface defects in the form of blisters, which can be seen at a temperature of 490°C.

Very well-known advantages of aluminum alloys, such as low mass, good mechanical properties, corrosion resistance, machining-ability,

high recycling potential and low cost are considered as a driving force for their development, i.e. implementation in new applications as

early as in stage of structural design, as well as in development of new technological solutions. Mechanical and technological properties of

the castings made from the 3xx.x group of alloys depend mainly on correctly performed processes of melting and casting, design of a

mould and cast element, and a possible heat treatment.

The subject-matter of this paper is elaboration of a diagrams and dependencies between parameters of dispersion hardening (temperatures

and times of solutioning and ageing treatments) and mechanical properties obtained after heat treatment of the 356.0 (EN AC AlSi7Mg)

alloy, enabling full control of dispersion hardening process to programming and obtaining a certain technological quality of the alloy in

terms of its mechanical properties after performed heat treatments. Obtained results of the investigations have enabled obtainment of a

dependencies depicting effect of parameters of the solutioning and ageing treatments on the mechanical properties (Rm, A5 and KC impact

strength) of the investigated alloy. Spatial diagrams elaborated on the basis of these dependencies enable us to determine tendencies of

changes of the mechanical properties of the 356.0 alloy in complete analyzed range of temperature and duration of the solutioning and

ageing operations.

Dispersion hardening, as the main heat treatment of silumins having additions of copper and magnesium, results in considerable increase

of tensile strength and hardness, with simultaneous decrease of ductility of the alloy. In the paper is presented an attempt of introduction of

heat treatment operation consisting in homogenizing treatment prior operation of the dispersion hardening, to minimize negative effects of

the T6 heat treatment on plastic properties of hypereutectoidal AlSi17CuNiMg alloy. Tests of the mechanical properties were performed

on a test pieces poured in standardized metal moulds. Parameters of different variants of the heat treatment, i.e. temperature and time of

soaking for individual operations were selected basing on the ATD (Thermal Derivation Analysis) diagram and analysis of literature. The

homogenizing treatment significantly improves ductility of the alloy, resulting in a threefold increase of the elongation and more than

fourfold increase of the impact strength in comparison with initial state of the alloy. Moreover, the hardness and the tensile strength (Rm)

of the alloy decrease considerably. On the other hand, combination of the homogenizing and dispersion hardening enables increase of

elongation with about 40%, and increase of the impact strength with about 25%, comparing with these values after the T6 treatment,

maintaining high hardness and slight increase of the tensile strength, comparing with the alloy after the dispersion hardening